Upgrading filter, suggestions?

[FroFro]

I'm wanting to upgrade Susan's filter to something gentler and well... of better quality. The filter that came with the tank was good enough to get it cycled, but I'd rather have something with a gentler flow so my betta can rest more comfortably near the surface, but still provides good filtration. The tank is a five gallon, I thought about maybe getting a submersible filter but I've read mixed reviews on them.

 

[Essjay]

I used to have a small internal in my betta's tank, one that had just sponge as the media. But the suckers finally became hard and the filter kept falling off the glass - and it's one of those filters where you can't remove the suckers to put new ones on. So I changed it for a sponge filter powered by an air pump. I would not use anything else in a betta tank now.
Because I couldn't figure out a way to attach the sponge from the internal, I fishless cycled the sponge filter in my quarantine tank. This also gave me time to realise that the pump created too much current for when it was transferred to the betta tank so I bought one of those little double taps to put in the tubing. By turning down the air flow to the betta's tank I can control the current and the second tap is used to bleed air into the room so there is not too much back pressure on the pump.
You can buy sponge filters which attach to the glass with suckers but after my experience with the internal filter I went for one with a weighted base (this one) - I didn't want to risk the sponge becoming unstuck and floating.