What is your favorite caliber

I have .177, .22 and .25. Haven't gotten to the bigger calibers yet, so can't speak to .30 and up. I'll rule out the .177 to start. Too light.

Like others stated, it depends on the use; however, if I had to choose one caliber and couldn't ever have another gun, probably go with .22. In the right gun it's accurate to 100 yards with upwards of 30 fpe, yet can be tuned down to 12 fpe for indoor or tight spaces. I have a .25, but it's just too much for tight areas, it really needs a backdrop.

.22 wins in economy as well. Pellets are 1/3 less cost than .25 and more economical on air usage.

as always, my opinion is worth what you paid for it. Take it for what it is, my opinion.
 
When I can, I like to shoot a lot, so .177 can't be beat there for cheapness. I don't plink at far distances either, so again perfect. I also like it being easy to quiet down.

When it comes to hunting, the only thing I hunt is ground and tree squirrels. For that, I've found my power-tuned .25 hits hard and makes me feel like I'm increasing the chances for a humane kill.

Over time I will become a better shot, I hope, and then I might go down to my .22 and even go down to my .177 for squirrels and see how that does. But for now, the security of having a lot of extra power makes me really dig my .25. Plus it's fun to shoot because it's a really good gun anyway.

So for now I'd have to say my most fun and best for hunting is .25, and best for plinking .177.
 
.20. 

I have 8 rifles in the caliber, 7 springers and a Silver Streak (for now anyway...lol). While most consider the limited choices in pellets a bad thing, I consider it a bonus. There might only be 7 choices currently out there and I have them all. I've never gotten why shooters think they have to have 15-20 or even more choices in pellets in a given caliber and it's usually the lame excuse used why they don't and won't own one. 

Those 7 are the best of the best and at least 3 or 4 shoot well in all 8 of my rifles. FWIW, I do own rifles in .177, .22 and .25 but .20 is my favorite.