Most of my tanks have multiple filters. All have either a HOB or an internal filter (Whisper "i" series). One also has a UGF powered with a powerhead. Another has a refugium setup, and another has enough plants that it could probably run filter-less.
All my tanks have UGFs with powerheads, my 125 also has an EheI'm 2028, and one 55 has a powerhead on the UGF and a HOB filter, the 55 gallon shrimp tank has two HOB filters, one is drawing water from the UGF.
The only frustrating thing about my set up are the MTS snails that get into the filters...this can't be good for the filters, and I know it must be traumatic for the snails....
I have a Tetra Whisper filter that is in-tank. I'm guessing it's considered a power filter, but I'm not sure. And on my next tank, I'm definetly going to get a filter that is on the outside of the tank.
I had an under gravel filter and took it out when I went heavily planted and upgraded the light substrate and co2. I have an EheI'm 2215 and half a dozen HOB filters of various makes and models the one I really want to get and try on my next tank is a biowheel I have heard good things and they look like a neat toy. They were on sale the other day $10 off and I was so tempted to buy one just to try it out.