There's really no compelling reason to stick with 72 mHz if you are starting out right now.

2.4 gHz is affordable now and getting cheaper.

Another thing is that gas engines are now getting smaller and more reliable. With the rising cost of glow fuel, more and more fuel planes will be going to gas. When you have an ignition gas engine, 2.4 gHz works is hands down the best way to go as it is immune to ignition interference that besets the lower frequencies.