I do seem to notice that more recent fans of the Gundam Franchise started watching from AU. I remember the first time that Wing was brought to the US. Most fanboys kept saying that Wing was the best and badmouths other older series (UC specifically). At least some of the fans nowadays are more educated in the Gundam Franchise.
Getting back on topic, My top Gundams would be God Gundam and Z Gundam. When I play SRW or GGeneration games, these two units are the ones I mostly use (hence upgraded the most). I wasn't that impressed with X. They didn't really explain the Category L4 ability of the Frost brothers.
Also, if you can notice, AU Gundams tend to be more uber powered in their timeline compared to their UC counterparts. This trend seems to be going away in more recent series which is good.
Now to answer Archangel Ashes question about choosing non-gundam unit, I would either choose the Sazabi or Queen Mantha. You really can't go wrong with Fanels.