I find the GDI/NOD officier to be quite lethal, especially again light vehicules and infantry.It's funny to out and destroy jeeps, buggies, rocket lauchers and the likes with a 125$ cost, that chaingun is quite good.
As well the basic rocket soldier is deadly versus vehicules.
In matches, I don't see much use for the higher costing class apart from the Technician, he rocks! Still cheap though.
Good players won't need expensive classes to be successfull at this game.
Although walking around with an ION cannon on your shoulder is fun.