Since you already have a semiauto pistol, I would suggest getting a .357 mag revolver. It'll give you versitility as well as a different type of 'fun'.
With that in mine, I highly recommend you look at the Ruger GP100 with the 5" barrel from Davidson's! Incredibly accurate, you can shoot .38's for target and reach out with the .357 mag round for hunting! With the 5" barrel, you won't quite have the nose weight that the 6" gives you, but you'll greatly increase your powder burn (velocity) and accuracy over a 4" barrel! The Ruger GP100 has several aftermarket grips available for it and Meprolight makes an adjustable tritium night sight set for it for home defense!
Tough choice, I've got a pair of Ruger Security Six's and i love em, and a bunch of 1911's, as said before you can always use the 357 for hunting where the 45 is a no-no, seems the ruger is a little bit lighter for carry, maybe to could work out a deal somewhere and get both
Just an idea to ponder, if you are looking for a full size gun to buy, if you are just looking to have fun at the range with a powerful snappy round check out the cz 52 tokarev which is chambered in 7.62 by 25mm it holds eight in the mag, it is a bottle neck cartridge just like the .357 sig, and it is only around $200.00. i love mine and it is a great gun
Both are excellent, but I have been on a .357 Magnum kick lately. Revolvers just flat out work. They don't malfunction often, they eat whatever you feed it, and there are some very modern revolvers.
If power is an issue, you can always just look for a few boxes of these, I think the difference would be negligible, maybe even a bit better in some cases, since the hole going in would be a little bigger.
For "ease" of operation, the revolver wins...however,
Shooting full power .357 loads in say a K Frame Smith will beat the gun. My first S&W M66 lasted about two years and that was after about four sets of cylinder hands and trigger components. I was shooting strictly full power loads. Of course, the K frame was developed to fire a few full house magnums and shoot mostly wadcutters or .38 powered ammo.
The L frame was next and took the pounding without complaint.
Full powered .357 recoil in 4" bbls. or shorter can be daunting. The recoil from a full sized .45 is a lot more negligible, and that .45 bullet goes in as a .45.