Deltecs are probably the best around. I have the Aquamaxx HOB cone skimmer and love it when it works. I have a problem with it overflowing. If I don't take it apart every couple of weeks and clean it, it is very inconsistent with bubble production. I also hate how you can't take the plumbing apart where the air enters the pump. I think that is where gunk builds up but you can't get into it to clean it out, they have it all glued together. Also, my propeller broke last year and I could never find one, so I had to buy a whole new pump that included the propeller. My last gripe is the bubbles. Mine puts out a lot of large bubbles into the tank and it keeps my lights covered in salt creep. I contacted Aquamaxx about the bubble and their answer was to direct the outlet in a different direction so maybe the bubbles wouldn't cause so much salt creep.
I have purchased a Deltec MCE600 to replace it and hope to have time to make the switch this weekend.