I have the 3 inch barrel so I am partial to that. However, you don't have the choice, so based on your post, I say go with the 4". Additionally, as you are new to revolvers, shooting 38 in a 357 may cause a crud ring to build up in your cylinders. You may find that you need to clean these more often than you would like, or would otherwise if only shooting 357. If you look around you can find cheap(er) 357 if the issue is $. If the issue is power, you can find many 357 loads. By the way, I don't know why folks think 38 is so cheap. I have found the prices diffs in my area to be negligible (or even more expensive in some cases). By the way, if you go for used, in addition to what another poster said here, ask or determine, if a trigger job was done. You may not like what was done to it. There are many threads here on Sp101 triggers. I would love to have a trigger job, but I dry fired the heck out of money, plus put a ton of 357 (and a small amount of 38) through it. This made the trigger much nicer (though not perfect) for free. I love my SP101, but the trigger itself is sharp, the hammer spur is sharp, and required serious force to pull it back until everything loosened up. My hands are large, so I got some Pachmayr grips and Metropol night sites (the front ramp has no color on it and is HARD to see against a dark backgrounded target). The gun shoots very accurate and will last forever. I love mine! You will NOT go wrong buying any SP.