Personally I really like the welterweight class. THey have the non-stop action and can go like the lightweights but have a lot more size and power.
205 is the most stacked right now (especially with the addition of Shogun), and 170 isn't too far behind. The weakest division right now is 185.
I agree, 170 is very good right now. I like the lightweights too. One division that is pretty good now, but gets underrated is the featherweight division. Not that its as good as 170 or 205, but it doesnt get much attention due to the UFC not having a 145 lb. weight class. There is the potential for some very good fights here.