There are loads available in your lfs and they all work on the same principle so you can't really get a 'bad' one.
One thing i would suggest is that you opt for onw which has not got a round cylinder on it. An angled or oval shaped one lets yo get into the corners easier and in between your decor and plants.
If you are carefull you wont suck up any fish or fry, they soon get out of the way.