A couple of sound smacks with a hammer on a punch, inside the cavity of a Torx or obstinate allen fastener will usually release it enough that normal tools will work.
But quality (Craftsman or better) drivers are a very worthwhile addition to your toolbox.

I've got a set of Snap-on Torx bits, one size is used only for removing rotor bolts, that insert has been replaced twice, and I've got a spare.
The other Torx bits are usually used for removing the rare stripped allen bolt, hammer the appropriate size in, and remove the bolt.

Torx was devised by the sadistic bastard son of Mr. Phillips.
Both of their namesake fasteners are best removed and relegated to the round file.