The original 1911's came with 7 round mags. That is what fits flush with the bottom of the full size grip frame. Sometime in the 1970's, I believe, the Devel follower (as currently used in Chip McCormick mags) was first used to enable the same size mag tube to hold 8 rounds. These mags also fit flush with the bottom of the grip.
McCormick PowerMags and Wilson 47D mags, two of the industry standards for mags, have slightly longer tubes and have an added removable base pad. They don't fit flush with the bottom of the grip, no matter how small you make the base pad. They work pretty well, but they are not really "true" 8 round mags, just a little longer than 7 rounders.
Next came Tripp Research CobraMags and Wilson ETM's (there are other's, but those two are the big players). These are true 8 round mags. They are longer than McCormick's PowerMags and Wilson's 47D's. In general, these longer tubes will work better as 8 rounders than the mags with shorter tubes as you can get a better spring and better follower in these longer tubes.
My personal opinion is, if you want a flush fit mag, go with 7 rounders. If you need to have that 8th round, you're better off with a mag with a longer tube.