By far my fave packy is the 3.5" from Early2Bed; search under packing dildos for Packy. In briefs it stays where it's supposed to, has nice balls, and is anatomically correct in size, shape, and feel.
For STP I have a 5.5" or else I'd pee on myself (okay, so I'm incoordinated!). But the 5.5" packy has very thin, flimsy balls, which makes it flip around in your shorts and gets annoying (IMO). The STP tubing makes it stay in place, or I suppose you could use a harness.
The Mr. Right Packy is far more expensive, larger, firmer, and IME will NOT stay put even with a harness. The balls are nice, but a bit too wide to fit between my legs nicely, so when I walk it makes the packy move to an anatomically incorrect location even with a harness. Plus side it could be used for sex in a pinch (hard enough to penetrate; possibly not hard enough to satisfy on the receivers end). The Lola Jake Cherry Packer looks nice, but is heavy and solid and not at all squishy and does NOT feel like the real thing. Stays in place, though. Lola Jake Sam Plus (Pack N Play) is far too huge for packing on a daily basis, the balls are way too big also, feels like a huge rubber hose in your pants and not worth the money (wanna buy it cheap? LOL)
Your mileage may vary.
Jay, King of the Packys