I am agreeing with Mainstream_Knot, there are way to many Faction servers.
Mini-Game servers are good if they are done right, Economic servers are fun at times, Try something unique. I also like servers with their own custom map on them (eg. Super Craft Bros, Death-Swap, etc.)
Do what you think is fun, not what every players always think is fun.
Here's a hint of a good idea that hasn't been done before (at least of what i've seen): Doom in Minecraft!
Hope that helped
