Assuming you're talking about '99 prelude sh over '99 civic si
Civic
- more roomy, trunk space
- lighter but not by much in comparison 400lbs?
- good hp, but low torque, you'll suffer when taking passengers going up 45 deg incline. 1.6L, naaaaahhhhhhhhhh
Prelude
- more cramped (especially back seats, better than eclipse back seats though. Well, it's probably just cramped in my 4th gen, dunno about 5th gen's rear seats.
- bumpy ride
- way more torque ( you know what that means)
- doesn't suffer as much as civic when A/C is on
That's what I think. All depends on what you're going to use it for, just commuting with max 2 people, then I'd take Prelude. But if you're also going to move stuff, and maybe take some people with you, I'd take civic si.
But in my position right now, I'd take prelude SH over SI.