In order for our bots to be as efficient as possible and be usable in as many different environments as possible, we're probably not going to see any humanoid bots. The sole exception to that would be if we needed some sort of psychological edge, in which case, mounting our bots in child-mannequin bodies would be ideal.
Nightmare fuel not withstanding, first of all we need to look at mobility. The ideal combatant is one who can be deployed in a short time, in any terrain and through a wide variety of means. So we'll want them to be reasonably small and light. This helps both with transport and because they're small, they'll be harder to hit. In terms of surface area versus volume, we're going to want them to be as close to a sphere as possible, giving us a maximal volume to hide important components while providing a minimal surface that we need to slap armor on. Unfortunately, spheres are annoying to deal with and tend to roll around a lot so we'll probably see something closer to a dodecagon (which co-incidentally, also looks an awful lot like the angular shapes we see on radar-confusing vehicles)
Allright, so we're looking at bots that are probably somewhere between a football and a beachball in size. I think that in terms of weaponry and mobility, we should be following the example of the A-10 Warthog. That is: half of our bot is firepower, the other half is dedicated to getting it someplace where it can deploy said firepower. I'm thinking a number of small ion thrusters, set in different locations in the chassis.
As for weaponry, since we're dealing with warbots in the future, we're probably building them either with high-end coil or rail rifles, with the whole of the bot built off a miniature reactor or big-ass battery.
Speaking of weaponry, some of our bots are probably going to be intended for short-term engagements and should be equipped with a battery of dumb-fire rockets for harder targets.