For a defense gun that you might want to carry concealed, the GP-100 with 3" tube is much better than the 4".
THe 3" barrel models have fixed sights which are low profile, snag free, look great, and are accurate. The grip on the 3" model looks like the same as on the 4" model, but actually it's smaller... just between the size of the full size GP-100 grip and the very small SP-101 grip. I think the grip on the 3" version is perfect and very comfortable. The 3" tube is short enough to pull quicker from concealment than a 4", yet longer than the "too short" IMHO 2 1/2" models. A .357 round can use the 3" tube a lot better to develop velocity than the 2 1/2. Expect about 35-40 extra fps with the 3" vs. the 2". Lastly, the balanc, pointability, and feel in the hand with the 3" model is awesome. It's my favorite Ruger, period. (I also have an SP-101 3" and a GP-100 4" adj. sight model). In fact I like it as much as my S&W 13's and 65.... and that's saying a lot.
BTW, my understanding is that next year Ruger will be putting internal lock/safety mechanisms in their guns... so if you want to avoid that, you might want to think about buying one of these sooner rather than later.
If you like them blued (I have one of these in blue also, just because I love blued guns) Davidson's has them on sale until January 15th. About $290 plus shipping dealer cost. Expect a dealer to add about $50 for their part. I paid $370 total for mine. My stainless model was about $80 more than the blued model.
This gun is very comfortable for shooting the .357 load. But for extensive shooting of very heavy loads and for target/precision shooting the 4" and 6" models offer more utility in that regard. Just another reason to own more than one of these beauties!