Imho IBO is probably the strongest series of Gundam I've seen so far, and I watched a fair number of them. The best thing about it I think is that it doesn't go batshit stupid in the second season, well, at the very least it hasn't done that yet.
What I most like about it compared to some other takes on the war is hell is that it doesn't neccessarily get preachy starry eyed nonsense every time shit gets bad. Folks recognize that it's shitty what they're doing but fuck it, it was the hand that was dealt and they're playing to the best of their ability. Especially in the second season, there's a handful of events that push some of the people and instead of taking the high road or acting brave or whatever, they show that they're human and perhaps don't deal with stuff perfectly and often get emotions in the way (especially since a lot of them are teens/young adults).
On Unicorn, it's beautifully designed and animated but the characters are such insufferable twats that I couldn't get past the first several episodes, and from that it really felt like they just took the worst shit from 00 and Seed and then made it even more cringe inducing. It's a damn shame really.
But if you just want pretty gundams of all kinds, watch Build Fighters because it's just that, people building model gundams from all eras and fighting with them in mock battles, it's silly and not entirely serious but good fun nonetheless.