My only problem going with the LS1 is that I LOVE Inline Six's.
But, I would also like to have 300hp, and getting 300hp out of an L-series is problematic for me. I fear Turbo-lag and getting that kinda power without a turbo leaves you with a high-strung, not-street-friendly, engine.
An RB26DETT would be a nice alternative, but the cost and technical aspects may be beyond me, or at least beyond the amount of work I want to put into it.
Chances are that I'll go with the LS1 or a NA L28 with as much street-friendly HP as I can squeez out of it.