I've made of list of pros an cons for the Return to Blockland Dedicated Hosting Service and Kaphost Blockland Servers.
RTB Pros
More user-friendly.
Has more features.
Soon will have automated donation system.
RTB Cons
Auto-save is very buggy.
Servers crash a lot.
Kaphost Pros
Six month service is cheaper.
Faster download and upload speed and lower ping.
One server alone is capable of holding 900 players (however, the record is 127).
Capable of holding 2,875 players across all servers.
Kaphost Cons
Requires FTP knowledge.
It's hosted by Kalphiter.
This is all I can think of off the top of my head.
I honestly lean more toward RTB.