So you are looking for the main return pump for the sump?
I would do around 1000 gph.....maybe branch it into two output locations in the tank.
You could also do 2 smaller pumps just too be redundant. If one dies or clogs, the other one would keep the tank alive for a little while.
Eheims are sweet.....but they are a little pricey. Being cheap and poor I end up with Rio pumps or Catalina (CA) pumps. So far it has worked fine but if I had the money I would upgrade.