One problem with the game is that as you complete missions, you unlock new mecha to use. Zeon has loads of different mobile suits. Depending on the mission you can take some long-range units like the Dom and Gelgoog, or some close combat units like the Gouf and Z'Gok.
The EFSF, on the other hand, has just a few units. Most of them are GM variants. They have no good ranged units... there is the GunTank, but just as in the cartoon there are only two types of this mecha: those that have been blown up already and those that haven't been blown up yet. Admittedly last night I did unlock the GM Sniper, and that is pretty decent, but it doesn't have the armor or the maneuverability of the Dom Tropen from Zeon.
Of course I do like the Zeon mecha better than I like the EFSF mecha, so I probably shouldn't complain that I've been finding them easier to use, but still... The variety gap between the two sides can be explained by Gundam's history as a mecha-of-the-week show. Every episode there'd be a new Zeon threat for Amuro to take out... but every week he'd be piloting the same old machine.
One last note. Piloting a GM Sniper and rushing into close combat against a Hygogg because your beam cannon is out of energy is not a happy fun moment.