Defi, blitz, the madddad gauge, autometer depneds what you want and the price... mechanical or electronical?
I have the Autometer Sport Comp Electric boost gauge w/ peak memory and warning light. Comes w/ 2bar (or 3bar?) MAP sensor that I can rig up to the stock system if I go standalone. 2 color condoms for light choice; green/red. I like mine
I've been really impressed with the Maddad V2 clarity gauges. Although if you want something cheap, I've got an Omori mech boost gauge for sale here.