Honestly, the best one to start with is likely either the first one (It's relatively simple and short), IV (same, but has a great story and characters), and VI (because seriously, shining example of FF right there.) All three of which can be bought for cheap if you have a a DS or PSP, or if you're really cheap you can get the original versions free of charge and play them on Emulators on your computer. (No I'm not supporting piracy, but the NES and SNES are both super old systems that no longer sell)
but since you're a PS3 owner, you can get away with buying VII, VIII, and IX, and they're all great choices as well, depending on what you're looking for.
VII is a pretty damn good rounded package, VIII is more character driven and has its quirks, and IX is old high fantasy style.
If you have a backwards compatible PS3, then I also highly recommend X and XII. X has what I feel is one of the best stories in the game, and the mini-game alone (blitzball) is enough to keep you busy for hours. Only real downside is a lack of an overworld map. XII on the other hand seems to get a lot of unneeded and unfair hate since it does things very differently, and most people can't be bothered to learn the Gambit system or are too hung up on how irrational the License grid is (in spite of the fact that it's a game and not reality.) That said, the game has a great plot, great characters, and honestly the most content of any of the Final Fantasy games. Plus it's really fun to play.
But that's enough of that.
I recommend playing the 2D final Fantasies first, as long as you're not some graphics whore who can't stand to look at the pixels or something. They're simpler and will be a fine introduction to the series.
My Console Library:
PS5, Switch, XSX
PS4, PS3, PS2, PS1, WiiU, Wii, GCN, N64 SNES, XBO, 360
3DS, DS, GBA, Vita, PSP, Android