My current build.
Esper, unstable genome, cyrokenisis, force wall, light manipulation, evil twin defect
18 toughness, 22 willpower, 24 ego
Take the tinker class so you get tinker I without needing any more int (which is really all I need, pretty much all the other stuff you tinker you can also get on your own at later levels, and being able to manufacture grenades are pretty much all you really need out of the skill anyways.
Cyrokenisis can't do as much damage as pyrokenisis, but being able to keep a enemy frozen for fifteen rounds is awesome and pretty much means that I can kill anything that gets frozen in the meantime.
The evil twin is pretty much totally negated by cyrokenisis, once he freezes, he can't do anything, but if you are frozen you can still use your mutations.
It lacks some firepower early game, but other then that once you get going its pretty much unstoppable as long as you play cautious (keep anything dangerous out of melee range, kill strong psysics and ranged with extreme prejudiced, make sure to use force wall as a sheild) from anything besides 1-hit ko's.
Its only real problem is that killing a swarm of things at once is a pain and requires quite a while, but as long as your caucious you should be able to kill pretty much anything.
My current (level 20) mutant with this build has Teleportation, Force Wall, Pyrokenisis, Sunder Mind, Stunning Force, Life Drain, Light Manipulation and Ego projection, and has pretty much done everything he can at this point (well besides going to get killed by the ape god or getting killed in the zone of death that is.
Other thoughts: Ego Projection mutation is pretty nice, while not turning you into the equivalent of someone who actually put stat points into it (since you don't get the skills, and you can only really raise one at a time), getting a 26 agi on a pure ego build is really nice end-game (egincannon with great accuracy FTW), same with being able to have 26 strength, and actually use your fullerite battle-axe with its actual penetration (even though you miss a fair bit) and kill stuff in 1 on 1 combat without bothering to use your psychic abilities.
Tap the mass mind allows you to raise two at once, so you will be near the equivalent or a regular warrior who actually put stat point into them.
If you get tap the mass mind to level 14 (which requires like level 27 or something crazy like that) then the cooldown is 5 rounds, or with a decent will score, more 3 or even 2 rounds.
You can abuse this by combinding it with ego projection to get your stats astronomically high.
Using a test build, I killed a salt kraken in melee my stats at the time were: ST:33, AG: 177, TO: 131, Dodge: 71, HP: 1974
Even with the best armor I could wish for still did 100+ damage per hit, but with 70 dodge he only managed to score one or two.
I usually start with low int and build it up slowly over time. Costs too much to raise attributes high.
The problem with that is that you will never be able to get any of the best abilities, and that by the time that you are able to notice the difference that starting with for instance only 18 ego (or 18 intelligence) has done you, you will already be level 10 and be underpowered and wont be able to advance as far as another who put 24 in the stat they need most.