Best solvents, if any?

I found a great product a few years ago to clean firearms called FrogLube. After it is applied, cleaning seldom takes more than a microfiber cloth wipe down. It contains no solvents, is environmentally friendly, and does not damage rubber or plastic. It comes in two forms, liquid and paste. I use the liquid to clean and the paste to lube. Application involves applying the paste, heating it until it melts and the metal is hot to touch (a hair dryer is sufficient to heat it), let it cool, wipe the leftover completely off. As for using it on airguns, I have cleaned a couple of barrels with the liquid. I ran patches through the barrel until they came out nearly clean. Then I put the liquid FrogLube on a patch and ran it through. It came out looking like the barrel had never been cleaned. It took about 20 more patches before they came out clean again. I also used it on my Condor a couple of years ago and it still runs like a champ. Since there is no residue left after application, I don't think that dieseling will be a problem. However, you should probably see if you can find any information from someone that has used it on a springer to be sure.
 
I have been using Krytech, a wax lube that was recommended by Tim at mac1. I understand that LD did allot of research with it and it has really helped in better groups when used as a pellet lube and to clean the barrel. I put 1 drop in the top and bottom of a pellet tin, smear it around with your pinky finger, add about 50 pellets put the lid on stir then a bit - add some more - continue. You are looking to just coat the outer edges of the pellet. You can get Krytech at the bicycled shops. They used as a dry lube on the chain. It dries and dirt doesn't stick to it.

I have also been using GunZilla on my firearms. It is similar to FrogLube. I have not tried it on any airguns or pellets yet.
 
If you mean just regular maintenance-type cleaning, I just use a bit of Simple Green (for really dirty barrels) followed by a bunch of dry patches on barrels. I also occasionally use J&B non-embedding bore polishing compound with a nylon brush, tho I do it sparingly and typically reserve this for new or really nasty barrels. The outside I just use good ole Ballistol, and make sure not to get it inside or on the seals, to battle corrosion. If I'm tearing one apart, I clean the insides with hot water and soap, then just lube the seal/chamber with silicone chamber lube.