I went may years carrying only a Leatherman Wave (original model). When I got back into "tactical" knives a couple years back, I started carrying one of those, too. I've recently started collecting slipjoints, so I sometimes slip one in my pocket in addition to, or in lieu of, a locking folder.
Favorite folders: Benchmade 710, Switchback, Ares, Mini Skirmish or 941; Spyderco Persian, Native III, Calypso Jr., Manix (for heavy work), or SS Cricket (for discreet dress carry); Buck/Strider Tarani; Al Mar Eagle Ultralight, especially in summer; CRKT M21-04 (for heavy work), Ryan Model 7, Bladelock II or Mirage Titanium Grey Ghost (for dress); Kershaw Blur (red).
Favorite Slipjoints: an old NYKCo. Teardrop Jack, Marble's Gladstone Teardrop Jack, Fight'n Rooster Cannitler, Bulldog Large Wharncliff Whittler, Schrade Old Timer 98OT Slim Stockman, Schrade Old Timer 61OT Large Slim Stockman, Sears Craftsman/Schrade Large Stockman, Case Tested XX Midnight Bone Sowbelly, Bulldog Five-Blade Sowbelly.
I own a crapload of good multi-tools, but the one I carry most often now is the Leatherman Charge Ti (with the extra bit kit), but I'll sometimes carry the old Wave, since it's much less bulky; or my SwissTool Spirit for the same reason, and for a change of pace; or my Leatherman Surge, if I anticipate a lot of rough work; or when I just don't feel like carrying big pliers, a Victorinox CyberTool Lite.