new here and ...to bigger tanks

[mamie]

Hi there I looked for you guys because the biggest fish tank I've had is a 30 gallon...I'm now venturing to a 55 gallon. What would you guys say is the best filter for that kind of tank? Also in my 30 I only have 1 9" gold fish he eats everyone in site. I want to go with live bearrers should I A keep gold fish in the 30 and put everyone else in the 55 or B put gold fish alone in the 55 and everyone in the 30??? by everyone I'm meaning guppies, platties stuff like that
I've always been partial to aqua clear filters this tank I'm purchasing used, for 100$ I can get a filter called a fluvial in tank filter for an extra 50$ (actually that 50 also includes 2 heaters ...but I already have 2 heaters)...