Yeah, allies are extremely boring cause they are so noob friendly. Allies always win (usually in early game)unless they choke big time, and when axis wins it is usually hard fought.

All allied units are stronger and require less Micro then their counterparts at their respective timing in the game, especially early game.
So in a 50/50 situation allies will win every single time vs their counterparts.

Allies also have easy counters for every thinkable scenario available from the start. DAK halftrack? Boys upgrade or bazooka squad. Are they in trouble? Press R. Meanwhile, the Dingo and 4x4 have zero direct counters and dominate every single early game (unless they mess up). Fortunately enough, these LVs also hardcounter the axis mottar, sniper and also MG which makes 3 of 4 options for wehr a huge gamble while allies can pull off whatever they feel like pulling off(pathfinders, 2-3x snipers/mortars, Engineer spam etc)

And if that doesnt work, why not pull up with some offmap barrages (only available early for allies) to destroy an mg which is causing trouble?

Late game the allies are so fortunate to have units that are generalists countering almost everything axis can field. Wehr for instance have 3 units that are generalists, the grens (which doesnt scale), the P4 which can easily be killed by almost every medium tanks), and the BG locked Tiger.

Guards, Rangers, SSF and commandos all are very effective against everything, while axis elites (gusta and stoss) have zero AT capability.
Most axis mediums also lack a turret which will make them way Harder to use effectively especially in CQB areas. And also very easy to counter with a sprint to snare or by other means due to not optimal pathing. 

Somehow allied players complain on the brumbar which is weaker than the bulldozer and mathilda due to lack of turret. They also complain on bunkers which can easily be destroyed by the offmaps available in every single bg except usf armored. Allies also have infinite vision capabilities not even needing to be close to the bunker at all to pull off these barrages. If a wehr player has a wall of bunkers, the allied players have messed up badly, end of story.

Allied players also complain about the loiters axis have, loiters can actually be shot down unlike all allied bombing runs from BGs or ASC. And allies have good loiters aswell, but all loiters and off maps should be tuned downs few notches. 

All of the offmaps and vision available to the allies are rendering a lot of stationary units unusable. Obice, bunker, flaks? Paradrop or vision ability to a nuke offmap ability destroying everything instantly. Somehow every single allied offmap also hits faster and stronger then axis do. Naval barrage, 3-4 second, zeroing arty like 10-15 seconds.. like wtf?

The fact is that allies require very little strategy to outplay the opponent due to everything they have being stronger and cheaper, which removes all the enjoyment of winning in a STRATEGY game. Its just spam infantry, tanks, arty or offmaps (usf ASC the call in simulator with zero counter as aa barely works on recon planes) so you win every single fight.
This is not fun for anyone, that one side is abusing stuff that doesnt have counters and can only lose if they mess up. Especially USF players can spam literally everything and get away with it. The percentage that searches for allies are the ones who wants to play in a sandbox mode, which obviously gets boring after a certain amount of time for most players.

Throughout the game cycle allies have been dominating lower ranks, and axis have dominated higher ranks in teamgames. This is clearly because allied players have been elo inflated by their ease of use and then meets true elite players that have grinded their way as axis, which is much Harder. 

Axis requires combined arms and skill in order to win, allies require spamming units, off maps and not messing up badly to win.

Which of them is more fun and rewarding?

Your mileage may vary but when I queue I queue random faction and usually the queue for 1's and 2's is a pretty even split.

Right now USF is very easy to play, but is not in a healthy state imo. People are crutching on armored and the Easy 8, Airborne tech skips, and WSC builds using the M1919 MG to crutch due to how stupid the buff to it was. The greyhound right now is outshined by most things and doesn't seem strong, the jeep is extremely weak dying to mainlines way too easily, while being unable to catch the ketten or krad if they are properly microed, even when ambushing them the opponent if half awake can usually get away when sitting there for even a few seconds. The Chafee is awful and completely outshined but the AT halftrack, mainly because it has terrible accuracy and timing.

Now back to factions using crutch/unhealthy strategies, with Wehrmacht, generally using Mechanized and spamming early game units and rushing out the Stummel to counter the horde of enemy infantry/mgs, and stalling till the Panther (which I would say can close out a game waaay too well atm if the opponent isn't seriously prepared for it). The Tiger is a menace, it is somewhat fair but it does have the CoH 2 bs of being able to one shot squads as it doesn't have a damage cap like most other vehicles in the game, meaning your vet 3 LMG commando squad at full health could just get unlucky and get one shot. Very engaging. Brumbar also is very strong, and as I mentioned the Panther is essentially GG once two hit the field if you still have a supporting army for them, as they will delete pretty much anything short of a black prince due to the armor debuff they give (It made sense to have it when you could only get one panther, it should no longer get that buff since you can build multiple now imo).

DAK still crutch on the AA halftrack, I have also seen in 2's the interesting camo blob of death using the new cloak focused battlegroup... UKF is still using callins mostly or the MP discount, though aside from some obvious weaknesses the faction is okay. It could use something so 2 sappers aren't mandatory for almost every build, the guy who said he only built infantry sections must be out of his mind as without the extra sapper you sacrifice a lot of capping power, too much in 1's.

Point is, the game has some serious problems that impact every faction, and some cheese strategies that lead to meta builds that I don't think are much fun for people to play against. USF is particularly egregious, the MG needed a buff but flat out damage resistance is silly, often when flanked instead of immediately trying to reposition you are better off just eating the bullets and continuing to fire while waiting for reinforcements, mainly due to how easy it is to avoid being punished.

The issue with MG's is that they don't use cover properly as someone else said, they almost never can be set up in green cover so the bandaid fix for USF was to just give it a flat out damage resistance buff. Fix the core issue by fixing the bug which hurts all mgs, then buff the USF mg in a way that is healthy in the long term, like more damage or a faster packup, more range, something that fits with the idea of cover being a staple of the serious, not some obscure one-faction rule on whether the MG is set up or not -.-.

The balance believe it or not has been largely better than CoH 2 was for a long period of time, but still there is a lot of work that needs to be done. The most recent patch changed vehicle pathing and my god, if it isn't significantly worse. Either way, a bit too much generalizing in the replies here for my liking :P