I keep going back and forth on this. When do I actually need an overstable mid? Sure there are times that I can't put enough zing on my zone and I can eke out another 20 feet? with a deflector, but if I really need to take that line, an os fairway like my mammoth or my raptor are much more versatile. The ogopogo is just a mammoth in eraser-like elastic performance plastic which sticks its landings. A month ago, I convinced myself that I needed the deflector to throw intermediate flex lines, and a week later changed my mind again after hitting those exact lines better with a raptor.
The only real trump card that an OS mid vs putters or drivers has is for slow panning, hard anny flex shots. Especially FH approaches. The wider diameter helps them catch air a little better and the beaded ones stick better than drivers or discs like the Zone. So for example, if your course has a basket on hard pan and you constantly have to flick around a corner to it, a disc like the Justice is just tailor made for you.
Here's a rundown of the ones I've enjoyed in the last few years (mind you, this is comparable to Three Putt listing his favorite max D drivers ((ok, not that bad)):
Justice - Not many mids fill the OS utility slot well by themselves but this one does. Really useful for folks with power FHs and like to flick upshots. Decent FH roller.
Quake - If you don't like beads but still need lots o' beef, this is a great one. Extremely comfy in FH grip due to lack of bead and low profile.
Anvil - Not quite as beefy as the 2 above but still solid. No bead, very comfy for FH. Like a wide diameter A2.
Recluse - Just tried one today. Quake beefy, Justice package. Decent glide.
Deflector - Like the Anvil but slower. MVP rim makes it a bit stickier than Champ/Lucid/etc type plastics.
Stego - This isn't really a mid I guess but I'm not sure it's really anything but the most stupidly OS thing I've ever encountered. The perfect upshot disc for those courses situated on Himalayan cliff-sides. :\
MOAB - More of a very slow FW driver but it's blunt and slow enough to be used as a mid, also wide diameter. Really OS, good FH roller.
Bard - More conventional shaped/speed OS mid. Some are close to being utility beefy, most are just workably OS throwers. If you get tired of Wasp stamps, this is a good clone.
Malta - Not so much (really)OS as they are straight-to-fade, goodly HSS. Smaller diameter makes them a bit glide averse and seemingly more OS than they are. I actually bag these most of the time. Bead is nice for placement shots, flatness and small diam. is decent for FH. Complements a workable straight mid like the Buzzz really well.