In my opinion, your budget will play a big role here and what your future intensions for the motor are. If your current vt is fairly stock, then as others have suggested i'd be looking for a new car with your motor of choice already in it. If you've spent a bit on it and would rather keep it then there's quite a price gap between the L67 and L98 conversions ($2300 as compared to $5000 as a rough guide). Naturally though, the L67 will be alot more 'plug and play' compared to the L98 which will require many more mods and parts changed to suit it so you'd need to budged for this (eg. exhaust, k-frame, tailshaft etc). You could save a little on this though with the L67 by using your existing auto box just with a 2600 torque converter and L67 flex plate, whereas with the L98 will require the gearbox to be changed.
Most members around here seem to prefer the V8 so I think that's probably the general concensus you'll get. Personally though, i'm going with the L67, though im biased
The L98 will have quite a bit more output in stock form, but the L67's don't take much to 'get up and boogey' either.
My 2c anyway...