Try a search on Z400 vs 400EX or something like that. Both are great quads, with the Z being a touch sportier and more powerful. At 5'4", you should fit either one well, but it is best to try before you buy. I have ridden with a few women of approximately your size and on Z quads, they held their own on the trails just fine.

 

I have an eight year old 400EX that must have 15,000 miles on it (still going strong!), and I just sold a Z400. The two are very close in terms of handling, in fact I have often described the Z as an EX knockoff with more motor. The EX motor will lug down and doesn't mind being ridden slowly, so it is a great quad for slower more techical trails. The Z's motor on the other hand likes to rev, so it makes a better choice for mixed riding in more open country. The Z motor has tons of hop up potential, with just a few simple mods.

If I were your size and weight, I think I would prefer to be on a built 300EX. The magazines did a piece on one that could easily beat a stock 400EX.

Again, will you be riding a lot of rocky technical terrain ??? You did say "ALL terrain", which makes it sound like you will be in the rough stuff. The Honda 250EX is a good choice if you are. It is based on the Recon (a small 2wd utility quad), and has shaft drive (nice for water and mud), pretty high ground clearance, and an easy to handle autoclutch. My kids ride theirs along with me when I ride the Rancher on nasty stuff in the mountains, and they handle it extremely well.