Depends on features you are looking for, technology changes fast. I own two of the popular ones, Escort 9500ix and Valentine 1 in my cars.
Both are upgradeable, Escort has GPS enabled, so you can reduce falses and it also tells you locations of red light cameras which is a nice feature. But V1 is much better in my opinion, its more sensitive Ka band, the ramp-up to full alert is great, cant live without the directional indicator, it has sucessfully detected laser many many times (but laser is hard to defend, usually when detector detects laser you are already caught). I highly recommend V1, cant believe how many of my friends have been saved after I pushed them to get this detector. They all drive too fast.
Your best combo is to get V1 + Laser interceptor gen 8 (Laser Jammer) if it is legal where you live. I run this combo on my daily driver.
'08 e63 M6 SMG SpaceGray/Black
'02 e46 M3 SMG TiAg/Blk
'85 e24 M635 5spd DiamondSchwartz/Buffalo