Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.
Some of these comments are very humorous. Face reality people; whilst the Holden 308 / 304 / 355 was a great, long-serving engine, the LS1 and later engines smack its ar$e every time. I've owned quite a few V8s (6 x Holden donk in HJ, HX, VP, VS & 2 x LS1) from circa-1975 cars up to what I drive now. Strangely, my car doesn't seem to have any low-mid or high torque / power issues and sounds like a V8 should.
To answer the OP's question:-
Economy - LS1 wins the race, even better if you get it tuned
Power - no brainer
My preference - should be obvious
As far as mod-ability goes, again, the LS1 wins every time, with cheap, proven and reliable power-adding being a very simple and non bank account draining process.
cheers