Hi cherry
I have an assortment of backgrounds on my tanks. The 55g tank has a black cloth background that I used velcro to attach. My 29g has a planted background, which is good when you do not have a lot of plants in the tank. My other 29g with the angels is kind of a theme tank, with a nice underwater scene of pompeii (sp?) and a dark blue substrate.
The all solid background will show up the fish much better IMO. But a planted background is very nice. Forget the fish backgrounds lol... they all look so fake, and what the heck? You have live fish in the tank to look at! lol..
good luck on your choices...

~ kate