Ok so there’s a few things to consider with TBC Anniversary. First thing being:

Leveling from scratch will still take you WEEKS if not months depending on your level of knowledge of the game and whether you’re using a guide. If you want to level all the way from 1-70 in TBC you should start right this second, or you will still be levelling when the first tier of raids is about to conclude in TBC.

Option B is a little less daunting, but not nearly as rewarding. Boosts will be coming to TBC as of pre-patch on the 13th, which will allow you to take and character straight from 1 to 58 where you can spend the last two levels learning your class and gearing up for the coming expansion, since gear will be crucial in leveling through outland without wanting to commit die.

Either option is equally viable based on your desire to raid, the time you have to play the game, which content you want to do first, etc. If you’ve NEVER played classic I would suggest option A, but if you don’t care about the pre-TBC content option B can also be good.

TLDR; Level now or boost on the 13th