Mechs or titans would be be a natural progression from combat suits. It starts out as a small combat suit for soldiers and get bigger and bigger. A Mech is a more natural movement if integrated as a suit rather than a tank, with articulated arms and legs, it can step over object where a tank cannot, if function like a suit it can be used in a mountain environment where tanks cannot. A tank needs a crew of three and mech needs a crew of one, and if operates like a suit would be more combat effective in target acquisition and get the round of sooner, however target accuracy may go to the tank.
There are a lot benefits a tank has over a mech, but versatility is not one of them. So where money is not a problem and the ability to only deploy a small number of units upon landing on a planet, with varied and different terrains that have not been pathed, my option would be to send in mechs rather than tanks, as a heavy weapons platform.
However I think plasma weapons attached to power suited soldiers would probably make both the mech and tank obsolete.