Outland vs Medivh. A non biased answer.
Many people seem to be biased about this. HERES A NON-BIASED ANSWER:

Outland:
5x exp, meaning getting to end content fast.
In game item shop for real money.
Cheaper training etc. (70% cheaper).
High in population (15k, though que sometimes nearly 3 or 4 hours).

In summary, it has a more private (custom) server feeling. A very fun and easy server.

Medivh:
1x everything, meaning slow, but true leveling experience. Leveling in WoW used to be rewarding, I think. (Some people already 70 though, despite the recent release).
Blizzlike server
5k players, but rising daily. No que time.

In summary, a more authentic TBC experience with a nostalgic feeling to it. You forget its not retail tbc. That said, way more time consuming.

All in all, if you came to warmane to have fun, see what it's like, and mess around at 70, go Outland! But if you're here to play The Burning Crusade, choose Medivh!