From wasted days trying to beat Endless Nights III, the Assassin was the candidate that my style of playing had the best chance to win. I tried many variations of an assassin class but have yet to come up with a real winner.
Some contenders are:
Ranger 9 or 10, Shadowdancer 1 or 2, Assasssin *.
Monk 9, Shadowdancer 1 or 2, Assassin *.
Rogue 9, Shadowdancer 1, Assassin *.
Bard 7-10, Shadowdancer 1-2, Assassin *.
The Ranger combo gives an extra attack per round by level 20, plus 2 more if using 2 weapons. Also some spells and bonuses
Monk gives improved evasion, better a/c, openhand combat and other useful feats.
Rogue gives a/c bonus through tumble skill, UMD and improved evasion. 5d6 sneak attack is not to be dismissed
Of course, if you add modules that allow HiPS items then you can add the following:
Ranger 9, Monk 1, Assassin *.
Two extra attacks, cleave, evasion, +2 on saves, wisdom A/C bonus et al means this is perhaps the best combo with HiPS.
This is because HiPS is awesome much of the time. Invisibility on tap is not to be dismissed lightly.
If you can get HiPS from another means then this combo has real merit.
Do you have a better choice without kit?