Your stats should represent what tree's you mainly use, If you just use several different trees then a balanced aproach would probably be the all round best. But if your like me, and specialise in one tree, then it's best to just pile all your points into the relevant
stat.
Assassins are very useful in a team, but on their own arent very good, unless te people they are fighting dont have evade combat. Pairing assassin with master knife thrower is also a common, and more effective way of killing. Focus adds ranged combat tactics and perception adds ranged damage, although not very much.
Martial Artists have really been hard done-by with the current system. They take too long to kill sometimes, and most people just roll out straight after being interlocked. However, their high resistence and health regen make them good "tanks" and when used correctly can be effective in pvp. I havent seen many martial arts and assassin loads, except for suplex and ki charged foot sweep. Focus is great for sneaking, but for MA (martial arts) its best to go with perception.
Sniper, when combined with expert rifleman is definately a long ranged assassin. It has moves that can hit people 30m away, it has high damage when using a sniper rifle, and can sneak around. It also has a lot of stun moves, which makes things a lot easier. Once again, focus is the way to go here.
A high belief goes a long way in any load. Belief gives damage resistence, although operative classes, as long as theyre leveled fully, have a high resistence. More importantly it gives dodge ranged, a redpills best friend, along wit Viral Deflection, wich is given by focus.
All reason is really good for is the IS regen, other than that its practically useless, and vitality gives you 10 health each level, so thats not very usefull either, seeming as health is rather easy to cap as an MA.
SO basically, its up to your own judgement, if i were you, i'd stay balanced for a while, until you know what tree you want to do, then when the reset hack comes out, put all your points into the stat that will help the most.