This is as subjective as you can get. It also depends on what you want to do with it. I'm not an expert so these are my opinions and are the world as I know it, I don't want to get flamed for this post, just trying to help out, who knows maybe my world is flat and someone else can help me round the edges.
12 guages are the most common, easiest to find ammo, accessories and do the widest variety of stuff with. These can be used for anything from dove hunting to clays to shooting big and dangerous game. This is because 12's come in 3 (4) flavors (2.5"), 2.75", 3", 3.5" with loads ranging from 3/4 oz of shot to almost 2 oz of shot and slugs from 260ish grains up to 385 grain.
16 gauges while making a bit of a comeback are still relegated to vintage and nostalgic type of shooters. In the 30-50's of the last century these were by far and away the gun of choice for most farmers, ranchers and the rural middle class. It's the perfect middle ground between 20 and 12 gauge. The 16 is thought to produce the perfect pattern with 1oz of shot. I for one am a big fan but do not own one and the biggest reason is they are kind of expensive to feed and also the different types of ammo just aren't there. Hopefully with Remington and Browning have 16 guages in their lineups this will bring about some of the ammo manufacturers to give us a wider variety of ammo. Another gotcha is that it only come is 2.75". Hopefully someone will make a 3" version and build some nice shells and start throwing multi-chokes in the guns and we'll all have reasons to go out and buy one.
20 gauge is the second most popular gun and the undisputed king of the uplands. This little gun can shoot a variety of loads and generally is a little lighter than the 12's, thus the reason uplanders like them. Accessories and Ammo variety are great for these guns. Almost any model of shotgun that can be had in 12 gauge has a little brother in 20 gauge. They also have the ability to shoot doves to deer and all in between.
28/410 - These are great guns and many a person has started off their shooting careers in the 410 bore. 28 guages are on most uplanders wish lists and the writers and TV guys extole the 28 gauges greatness. For the people that put 20,000 rounds a year thru a gun 28's and 410's are generally the choice. They don't offer much by way of recoil but they also don't offer much by way of ammunition variety from the factory loads. These guns also have large and loyal followings amongst the handloading set because both can be beefed up enough at the reloading bench to give them enough oomph to take game up to Pheasant size and still be light enough to carry 5 days in a row. These guns can get very expensive to feed because once you figure out your effective range with expensive factory loads you'll not want to shoot anything else, then you'll run out and buy a reloader, then you'll be hooked. I've read more times than I can count of people with that shoot alot of shotguns at the end of each year having a bigger pile of 28 gauge hulls than all others combined. The gun on my wish list is the 20/28gauge combo Franchi Veloce and I will own it some day.
12 guages are the most common, easiest to find ammo, accessories and do the widest variety of stuff with. These can be used for anything from dove hunting to clays to shooting big and dangerous game. This is because 12's come in 3 (4) flavors (2.5"), 2.75", 3", 3.5" with loads ranging from 3/4 oz of shot to almost 2 oz of shot and slugs from 260ish grains up to 385 grain.
16 gauges while making a bit of a comeback are still relegated to vintage and nostalgic type of shooters. In the 30-50's of the last century these were by far and away the gun of choice for most farmers, ranchers and the rural middle class. It's the perfect middle ground between 20 and 12 gauge. The 16 is thought to produce the perfect pattern with 1oz of shot. I for one am a big fan but do not own one and the biggest reason is they are kind of expensive to feed and also the different types of ammo just aren't there. Hopefully with Remington and Browning have 16 guages in their lineups this will bring about some of the ammo manufacturers to give us a wider variety of ammo. Another gotcha is that it only come is 2.75". Hopefully someone will make a 3" version and build some nice shells and start throwing multi-chokes in the guns and we'll all have reasons to go out and buy one.
20 gauge is the second most popular gun and the undisputed king of the uplands. This little gun can shoot a variety of loads and generally is a little lighter than the 12's, thus the reason uplanders like them. Accessories and Ammo variety are great for these guns. Almost any model of shotgun that can be had in 12 gauge has a little brother in 20 gauge. They also have the ability to shoot doves to deer and all in between.
28/410 - These are great guns and many a person has started off their shooting careers in the 410 bore. 28 guages are on most uplanders wish lists and the writers and TV guys extole the 28 gauges greatness. For the people that put 20,000 rounds a year thru a gun 28's and 410's are generally the choice. They don't offer much by way of recoil but they also don't offer much by way of ammunition variety from the factory loads. These guns also have large and loyal followings amongst the handloading set because both can be beefed up enough at the reloading bench to give them enough oomph to take game up to Pheasant size and still be light enough to carry 5 days in a row. These guns can get very expensive to feed because once you figure out your effective range with expensive factory loads you'll not want to shoot anything else, then you'll run out and buy a reloader, then you'll be hooked. I've read more times than I can count of people with that shoot alot of shotguns at the end of each year having a bigger pile of 28 gauge hulls than all others combined. The gun on my wish list is the 20/28gauge combo Franchi Veloce and I will own it some day.