Hi I can recomend the Spektrum DX6I 2,4ghz10 model memoryis very good for both Tanks and Boats(even aircraft if you wanted).
First question you need to answer is how many channels will you need (four is normal for Tanks)The Spectrum has six channels buttwo of them are on off channels (turn on lights, radar, that sortof thing).The more channels you need the price goes up fast,double if you want eight channels, double again if you want twelve channels.

regards pete