A tip: freezing a Squirrel Dude like a Kong will equal up to 90 mins of work vs. the max 30 mins in a Kong - the little prongs are awesome.

We have the Kong Wobbler and I find it too simple for my pups. Despite being heavy, Kes picks it up and lays it over to get all the food out in one motion lol.
Toys mine like:
Linkables (great for Z, but not durable enough for Kes to be used unsupervised)
Canine Genius Leo and Mike (too complicated for Z when linked, but perfect alone for her and Kes enjoys them linked as long as the necks aren't exposed to gnaw on)
Tug A Jug (too difficult for Z, but Maggie and Kes love(d) it, we just have to replace the rope periodically - not good for unsupervised play and can break things if used by a dog who likes to shake toys - Kes bruised his thigh badly enough to be 3 legged lame for about 30 mins at one point!

)
Squirrel Dude (durable enough for Kes unsupervised, great with dry treats or frozen stuffing)
Tricky Treat Ball (soft rubber so not for unsupervised play with tough chewers, but the most difficult treat ball I've run across)
Treatstik (very durable, tho Kes can make marks on it, holds dry treats/kibble well, fairly difficult, requires different motions than other toys)
Waggle (Very high on the difficulty scale, but Kes seems to have a knack for shredding them, though Maggie never damaged hers. Too tough for Z.)
Biscuit Block (similar to the Football in the same line) (Perfect for dog biscuits, not ideal for heavy chewers since it's technically a puppy toy in the Busy Buddy line, but if you go to the largest size it'll work for a BC-size dog. Maggie loved hers!)