Not to be too blunt, but there are a few threads about this topic already.
WarCryer - party buffer
OverLord - Alliance Buffer
Unless you are going to play to the end game, WC will get you into more parties, easier and your solo capability is greater.
OL is for Seiges, Raids and large PvP.
Both are awsome characters but you need to know what you like to play too. OL's are tied to their clans and Alliances. WC can party with anyone, any time.
Depends if you like to play with people alot or if you like to party sometimes, but still go off on your own once and a while. Overlords depend on clan support, Warcryers have a little more freedom.
I have to say it was quite fun on PTS when we did a good pvp party. I went in first to get "aggro", popping my hero UD and then spammed cp cures / hop until all 9 Thizznation members were dead and all 9 of us were still alive. Lather, rinse, repeat.