I've been on both sides of the fence too and I agree with fl327, the turbo 6 is funner. Not to say a V8 Z is boring, it certainly is not. I'm just taking into account the whole package. Driving, tuning, planning, noises. etc. My V8 Z was faster but I'm having more "fun" in the turbo Z because of all the other factors. It's up to your personal preference and what you feel comfortable working with.
To begin with, I think the L28et will be cheaper because of less fabrication and trannies are $50 but do you really count how much you spend on your Z anyways? You're gonna get sucked in no matter what engine you choose.