2.4 ghz for sure!!! the issues with electric helis plus interference with the mhz stuff are legion.
I stuffed my Trex into the deck because of this...and wont fly it again till I get a 2.4 ghz radio.
The Trex is an amazing heli otherwise, copes well with a strong breeze too...it outpunches just about any other small heli...of course there are some other makes but you will pay more for them.
I agree about the gyro thing...the basic gyro is still better than what was about yrs ago.
The Belt one will do the job, maybe a better servo will help but I wouldnt go too mad on spending....though do buy the 2.4 gig radio...and fit it. The setting up will be educational for you...just make sure to DISCONNECT the main motor wires ok?. so when you go through the setup you dont start the thing up and ruin things
Rob