If you had to choose only one rc to keep from all the RC you've had

[TexasSP]

I would probably keep my SCX10. Not fast, but setup to run submerged and manages to get around on all types of terrain. It's a blast because there is some challenge to it being solid axle and all. The scale appearance helps too.

[trev3813]

I'd keep my Brushless mini revo, its waterproof fast and doesn't break much :D

[Ola]

I try to keep a 2 car rule.. It might be 3 for a while, but then 1 gotta go hehe..

It`s not that i havent got the money for more, but it keeps the hobby room tidy, the wife happy(ish), the cost`s goes down (since i gotta sell one to buy one), and perhaps most important; i havent got time for more anyway ;)
When i get bored of one, i sell it and get the joy of buying a new.

The modded E-revo BL is on top of my list right now, but havent owned it more than 4 months yet. (just got back in the hobby after a couple years of changing diper`s and wrenching 1:1 turbo`d streetcars...).