Striking scorpions are my joint favourite hand to hand unit in the eldar, along with a seer council.
I know a lot of people prefer banshees, but if you are building an all comers list, scorps are better. More attacks, higher strength, better saves. Exarch has access to a powerfist and a relatively okay gun. [okay its s6 but it avoids wound allocation issues]. I wouldn't bother with chainsabres, although the biting blade thing can be good against tanks/dreads.
Edit: Because I am sad, I actually spent an hour rolling some dice for imaginary hand to hand combats, with 10 banshees w/exarch with executioner vs 10 scorpions w/exarch with scorpions claw against various different units. Against marines, provided the Exarch actually hits, you only do slightly worse with scorps than you do banshees, and against anything weaker, you do a lot better.
Scorps should be able to go toe to toe with assault marines and win. The problem IMO is that eldar aspects should be more on par with veterans than bog standard marines, but this is an issue across the board with eldar.
I still say take a powerfist over a lightning claw. If you play a few games, you will eventually get frustrated with the wound allocation rules if you take something striking at the same time as the rest of your unit. Obviously on terminators, this is not an issue as they all have power weapons. I actually have five lightning claw chaos terminators and a lightning claw terminator lord, so it isn't that I dislike the weapon, its just striking on initiative with power weapons in the current rule set is not optimal unless the whole unit has them.
I made my own raptors from assault marines and chaos marines
They are traitors from the "Crimson Ultra Fists" chapter [because in my gaming group we have Ultramarines and Crimson Fists, so my chaos raptors have a mix of their paint jobs.