The STS are the only ones worth keeping for ease of reloading - unless you want to reload slug- but the latter can be a PITA for ironing the mouth ( if you go to antique shops/sales you'll often find for cheap mouth ironing tools from the days when shells were sealed with a casemouth wad) . Winchester AA's as described above are good too.
I would look at the economics of relaoading 12 ga. If it's acceptable for your accuracy needs, buying flats of economy 7 1/2s or of #6 game loads can be almost the same cost as buying powder, wad/shotcup, primers, shot... I looked at it a couple of years ago when flats were in the $40 to $50 range and it made my time worth about $1.50 an hour in savings.