Luisfc: It depends. For me, I began with 3 R5Bi's. A year and a half later, I tried out the towers and was surprised there wasn't a greater difference. With the R5Bi's you're going to need a good subwoofer. With the R55Ti's, you will also need a good subwoofer, but it can wait a bit. The towers are 3 dB more sensitive, so you can play those louder than the R5Bi's (but I found the R5Bi's got more than loud enough for me). I'd rank the R5Bi's as a bit better for music, while the R55Ti's a bit better for movies. Others will rank them differently.
Music area: Magnepan 3.6, McIntosh MC2205 amp & C48 preamp, SVS SB13-Ultra, Oppo BDP 95, dbx 3BX, and assorted equipment.
Movie area: EMP Tek E5Bi (were rebadged to R5Bi), RBH/EMP Tek R55Ti, PSA S3000i, Denon X2000, Oppo BDP 83.