I'm a shaft drive guy, my Ascot and VMX. The pros...low maintenance. The manual calls for first service and every 20k miles (give or take). But I change it every service. It takes five minutes and its cheap. The cons...no gearing changes. Unless you talken money.
Chain Drives...pros..affordable gearing changes. Give the girl a new character! And hey, chain and sprockets are a maintanence item any way. cons...At some point, you will have to replace them.
Belts...pros...it's proven and its clean. Less adjustments than a chain. cons...more expensive to change gearing.
All the aboved mentioned final drives are all reliable if maintaned properly. If not, chains break, belts snap, and shaft drives implode. Do not let this be a big factor in deciding what to buy. If the bike grabs you, let it.