{Hmm}. The usual stock advice you are going to get, is to go to Asura. If you're going to do that, I suggest doing it quickly because transfers are cheap until the morning of the 31st. Asura is the most populous server indeed, and you are more likely to find social interaction, linkshells, etc there.

I've never been on Asura myself, but that's what everybody suggests doing. I recommend you sticking with your main; getting up to 99 as a new character is not impossible, but yet I don't know if there'd be all that much to gain by re-rolling. You could, however, piddle around with a mule if you want to experience early-game again, or even a new Lv1 job (as there are many jobs that were probably added since you last played).

I got a new player walkthrough over on FFXIclopedia that is almost complete which should help you get into the game easily. It's a gradual thing, and it starts off with basic stuff and eases into new stuff instead of giving a huge info dump all at once like other guides do.

Either way, I hope you have fun!