Eenie, meenie, miney, mo....
Seriously, though, when I first started out it was as Ira said 'Ooohh... that's nice' only to find that it is incompatible with either it's new tank mates or the setup, so you set up another tank for it and then buy it some allegedly compatible tank mates, but they chase eachother around and one gets tattered, so you set up another tank, and... you get the picture...
Now I am more fussy - I research the fish and try and set up a biotope tank for it. Mind you I still have three tanks with guppies in that have plants from all over the place that I do not have the heart to get rid of...