I've heard a lot of good things about the rc18t, all the reviews are good. Lot's os speed and good components right out of the box.
Personally, I can only give a recommendation on a mini-t because I actuallyhave one. I absolutely love it although, it took a couple hop up for me to enjoy it as much as I do now. I couldn't believe how long it took for me to actually break it, very durable.
If I were in the market to buy one or the other I would defiately go with the RC18t, jut a better value overall right out of the box. There are some other new 1/18ths on the market as well that deserve some attention although not quite so popular. If you're lookin to spend quite a bit less money I think the Itsy Bitsy spider is worth a look at.