Good question. I can give you a few things to consider based on my experiences.

SIG P220--I carried a SIG P220 as a main duty pistol for several years in the 90's. It looks good and just plain feels good in your hand. If you've been spoiled by a Colt Government, you'll like how this gun feels in your hand. It's a single stack magazine (thinner) which makes the magazine well and grip thinner in width. It shoots very well but the double action pull on the first shot is a little heavy and long. The single shot trigger after the first shot is awesome. It has a 7-round magazine unless you buy/change to extended mags.

My SIG was blued so it sucked keeping the finish dry when it rained (cops do have to get out in the rain). I carried it in a duty holster on my duty belt and in a gun bag off-duty. Like any blued gun, the bluing can get a little worn and you want to take care of it. I've worn it in a belt holster while hunting which was similar to my duty holster. SIGs cost a little more and have that long double action trigger on the first shot but they are a great gun.

Glock 30 & 21--I've carried a Glock 30SF on duty in a belt holster (usually concealed by a Cabelas 3-season jacket or fishing vest) for 3 years now in a plainclothes assignment. This is smaller than the full size Glock 40 (Model 22) I carried on a duty belt for years and it sometimes feels like it's not even there.

Like all Glocks, it has that single action (Glock calls it a safe action) trigger pull for the first through the last shot. Glock barrels ride lower to the grip and your hand/wrist so you don't get quite as much muzzle climb (something that's not a big deal for me but it is for some). Glocks have an ugly but extremely weather resistant finish. I once saw a guy demonstrating shooting a Glock pistol underwater in a Las Vegas hotel swimming pool at the Soldier of Fortune Convention (it had the underwater firing pin and cup designed for that). I never had to worry about the finish on my Glock getting ruined in the rain.

The Glock 30 is what most people would refer to as a compact pistol as opposed to a full-size (normal duty weapon). The compacts are designed to be a little smaller and easier to conceal. Essentially, a compact is a little over an inch shorter.

I've shot Glock 21's several times at the range (it's the full size Glock .45 pistol) and used to carry a Glock 22 (full size .40 caliber Glock pistol) as a duty pistol for years. I even carried a Glock 27 (.40 caliber) subcompact) as a hidden backup weapon for years.

This Glock (30SF) stands for a "Slim Frame" model where they flatten the backstrap (somewhat like a Colt Gov or SIG) and thus reduce the grip circumference. The new generation 4 Glock pistols allow you to switch out backstrap parts so you can better match the grip to your hand (it used to cost you an aftermarket pistol-smith job to do this).

I've shot all of these pistols and find each of them shoots very well. I don't think you'll go wrong with any of them. My advice to you would be to ask your gun store sales person to let you handle each pistol and see if he/she will let you try the different backstraps on a generation 4 Glock to see if one fits best. If you have friends who own each gun, ask if you can shoot each one. That will give you a good idea on what feels better and what you can shoot better.

Last, but not least, consider what you plan to use the gun for. Hunting? Open carry? Concealed carry? See if you can try putting the various guns in your type of holster, gun bag, etc. That may give you another aspect to consider. This is a little long but hopefully this information gives you a little help in making your decision. Good luck and let us know what you decide.