I was going to redo my Soundwave to more closely resemble G1 but maybe I should hold off. For me the 3 main Decepticons would Megatron, Soundwave and Starscream.
Megatron is a bit of an interesting one as I'm not sure Lego would be keen on making the gun disguise as it was quite realistic. So the tank variant (similar to mine) would probably be the direction they'd go.
Would be nice to have 3 of each. Not sure who would be the third autobot though (not Blaster, as he's too close to Soundwave).