I own several Hilti tools.....My favorites are the TE 76 and the DX 460 for sill plate shooting.
I would not have even considered a smaller jack hammer for this job except that the Hilti's i own impress me and i was trying to talk myself into buying the Hilit even though it probably isn't the best or fastest tool for the job I'm faced with.
It all depends on your slab..
If you can saw cleanly through (4-6"), the hilti will quickly snap the cutout into manageable pieces.
If your saw cut's a little shy, you'll end up pulverizing to get it out. Then I'd rent a big electric.
I've done a LOT of this with my ts400 stihl and a te76 (i think). I've even put duct work under a slab this way:shutup:
edit: IMO Hilti makes the best electric rotary hammers.:thumbup: