I can speak from experience on this subject. I have used only UGFs w/power heads for years, back to when I first started 20 years ago. I just got back in this year (1/1/9 to be exact) and set up my old UGF
to find out that it's becoming a thing of the past.
It really comes down to preference. UGFs have to be maintained by weekly gravel vacs especially if you have a lot of fish or dirty fish. The gunk builds up under and you CAN get it with deep gravel vacs. You have to limit your decor to not block the filter plate and power heads are a must.
I decided to switch to a canister filter, mainly because I'm doing a planted tank and I want to get better growth, but also because it's pretty heavily populated and the gravel vacs were getting to be a huge pain. Right now, I have 1/2 of the UGF
still running, I pulled the first plate after 1 week of running the canister (threw some established gravel in with the bio-media) and am planning on pulling the other half this weekend. during my water changes and gravel vacs I have noticed that the half running the UGF
is still nasty, and the half without has hardly anything bad coming out of it, just some still solid waste in the upper 1/2 inch that comes out with just running the gravel vac across the top of the gravel. I consider the canister a godsend!!
I went with a Marineland C360 for my 55g, if you want to check out my thread about the different manufacturers I go into pretty good detail, lots of research
Which canister filter should I choose?