If you don't want to buy one of each you probably need to decide what the proposed use for the gun will be. If you're mostly a target shooter the .177 is probably the best choice. If you plan to use it for hunting your likely game and expected shooting distance will probably be the determining factors.
Marty, our PS is in 177 and I do love it for my offhand shooting, which is one of the reasons I bought it, given the TX versions are more muzzle heavy. I like the balance on the PS, better, for the sake of carrying, too. Still a heavy gun, though, for this old granny. I've been tempted to tune it down a bit, though, because that very center balance makes it a touch muzzle light, so I have to pay strict attention to my follow through. Going with the heavy 10 grain plus 177 pellets seems to calm it down a bit. Given the heavier weight of the 22s, that might do the same. Just a thought. In the end it really depends on how you'll use the gun, I suspect. For long range work, I do prefer the 177 for the sake of trajectory, but we're strictly target shooters, not hunters. I certainly don't think a 22 would be a bad choice, but I have never shot any AA in that caliber.
Marty, the bulk of our outdoor shooing is at 30 yards, these days, since that's a good fit in our backyard, but we have extended out out to 50 yards at time. That's a bit tricky though, since our 7 plus acres is heavily wooded. I am very comfortable with the Prosport at 30 yards, of course, and at that distance it's mostly offhand work. I have guns I like better for shooting off the bench, but I have pushed our 177 PS to 50 yards to test for accuracy, shooting from a rest. It certainly shows it's AA lineage, here, using a couple of different pellets, wind and all. Easily a 50 yard springer, in my book, with the right pellet. Never would have guessed it likes the Crosman domed, but you never know until you try.
i had a prosport in .22 that shot JSB 14.3 at 740 fps. zero twang or vibration and was able to do 1 inch spinners at 45 to 50 meters from a sitting position, rifle rested on my knees. it is now in the posession of a friend who lowered the power to about 11.6 fpe and shoots jsb 15.9. he shoots at 50 yards and from the bag can easily outshoot my groups. it has become ever more pleasant... that level of accuracy can hunt at either power level. But it is because it can achieve that level of accuracy. I think that the .22 is better at bucking the wind so target shooting can be done with either caliber. .22 is easier to load and seems to be smoother when shot at lower power levels... my .02.
May not get better anytime soon either, GBP has been rising against the dollar again recently. I agree that there certainly seems to be limited inventory also which never helps with prices.