Welcome to Librarium Online!
would you choose a squad of wraiths or a squad of 5 scarab swarms?
Neither can be chosen by themselves, a Necron army needs at least 1 HQ choice and 2 Troops choice.
...seriously, what's the point numbers of the game? What are the other units in your army? Do you have an idea against which opponent you'll be playing? ...etc.
Well since the squad of wraiths is probably 3 of them, thats 123 points vs 60 pts of scarabs
not much of a comparison
Personally i like to take scarabs, however I've been considering dropping them (and my heavy destroyers) for wraiths in 5ed. It depends on what you want. Wraiths are excellent light infantry/vehicle hunters. Scarabs are for tying up enemy units and eliminating light infantry.
The survivability of the two greatly varies depending on what armies you're facing. Try both out against several opponents. Wraiths use in squads of 3, always, scarabs can be any number you feel like fielding though. Both you need to get the charge with, and having jetbike movement they're good at it.
Its not a points issue its a FOC issue, im woundering if feilding a second squad of scarabs instead of wraiths and my destroyers take up the other fast-attack position
You could take a full squad of scarabs instead of a squad of wraiths for less points, and I certainly would.
My gaming group's new motto: That army you're using is overpowered because it hurts my guys, codex is broken and needs a rewrite.
Wraiths only work well in multiple groups of them, and best if accompanied by a destroyer lord with a res orb. You're looking at a CC squad that has 3 wounds between it, and is T4. The invuln save doesn't help you there; they're nothing but bolter bait unless there's a minimum of two squads together.
Take the scarabs. Max em out. They'll be your tarpit against an opponent of choice. (Counter-charge, tie up heavy weapons, whatever you need them to.)
Assuming your army currently contains neither, I would first add scarabs. They're really almost necessary in my mind.
With Necrons having alot of trouble in CC in 5th, I think having those fast, cheap, effective scarabs to prevent any horde of elite close combat threat from getting to you or tie up, even temporarily, will help you to shoot what needs shooting, and no get overrun.
60-120 points on scarabs won't ruin the phase out.