BDS doesn't make a 2.5" lift, they have a 2" or a 3.5". They have a lifetime warranty. The only lifts that I personally would recommend are the BDS or OME. OME has a reputation of having some of the best flex and nice street manners combined and aren't going to sag in a year. If you look around the forum you will find that there are people that are still getting sagging issues with the new RC lifts.
As Jarred said also, if you go with the 4" you will have to go with a t/c drop at minimum or put a slip yoke eliminator and CV driveshaft in, which will add another $300 minimum if you can make your own driveshaft or you could spend $300-$500 on an aftermarket one plus the $200-$250 for the SYE.
I had worn out flat factory springs and my rear gas shocks were shot to the point that when I removed them they didn't expand. When I replaced my suspension two months ago I never realized how nice of a ride I could actually have in my YJ. It's still not a Cadillac but it feels damn close compared to what it was!
1997 TJ, 5" IRO front with 4.5" HD IRO WJ rear, 35x12.5x15 Mickey Thompson MTZ, JKS disconnects