Even with all of the legacy warzone exp boosts, it took me 8 day 8 hrs played of warzone leveling to get to 50 on my alt.
The upside is that you can max your warzone commendations before hitting 50 (3500 rwz comms, 2000 wz comms).
Still, it's much faster to level to 50 with quests and space mission dailies. It takes about 4-6 days played if you take your time through quests. If you're speed-leveling, you can space bar your way through quests and get to 50 with two days played.
Ok I was getting ready to say "4 to 6 days /played?" but then you followed up.
The legacy exp perk basically puts you back at the amount of exp you used to get for WZ's. Not sure when it happened, but at some point they reduced exp acrost the board. (then again I might be remembering beta levels)
The biggest problem is that leveling this way is entirely queue dependent.
When you're going through class and planetary quest lines you don't have to sit in a queue.
If you only play during 'prime time' hours then it isn't bad.
What I generally do on alts is PvP while the gettin's good, then when the queue slows down I go back to my class/planet quests.
The upside of this is that you pretty much stay a couple levels above your quests, which makes them quick and easy to run through.
In fact I would say the fastest way to level is running class/planet missions with PvP/space missions as fillers in between planets or any time you fall below your quests listed levels.
But the real "best" way to do it, is to play what you enjoy and let the levels take care of themselves.
I'm up to 5 lv 50's now and the 'desire' and/or 'excitement' of gaining levels just isn't there any more.
When I'm playing my lower level alts I'm more than happy just to run around killing this or that and sooner or later I might run acrost my quest mobs. Streaking through a WZ. Taunting opposite faction players outside their outposts on som planets. If I happen to level up that day 'great', if not....'great'.