Do you mean the hang-on-back type or canister? For HOBs, I'm a devoted fan of the AquaClears. Simple, well made, and lots of choices for media. I have some that are older than many people on the forum.
Have removed my internal filters from my Juwel's and replaced with the external Eheim 2026 (adjustable flow) in one and the Eheim 2324 (with thermofilter) in the other - both fantastic. Eheim are quite pricey, but well worth it - none of the constant filter maintenance, plus they're very quiet (had to keep checking that they're actually on when I first installed them!).