I have two friend which both have two oscars. They don't do much.
Red Devil's color changes very often therefore they are more interesting to watch as they grow up. You need to be picking when buying them though because Red Devils looks so much like the Mida Chilad that alot of crossbreeding has happened between the two. It is good that you have a 55 because the is the minimum for a Red Devil!
The thing with Red Devil's is; they need to be kept alone or with mating pairs. They can't grow up with eachother. If you got the oscars then you could get two or three.
Driftwood and rocks are a good decoration for Red Devils but you need to be careful and not have to many because Red Devil's are careless and will run into a rock or piece of driftwood and really hurt themselves. You can use regular pet store gravel but sometimes when they shuffel through it they will hurt their lip, same with Oscars. So I recommend a fine gravel or sand. Don't use plants (real or fake) because it will just be redug up by your red devil and maybe oscar.
A variety is essensial to Red Devils. Go to this site to find out more;
http://www.worldcichlids.com/fishprofiles/reddevil.html
Just put that address into your web browser.
If you want to know more about Oscars then go to this site;
http://www.oscarfish.com/
I think that both are really pretty! Hope I helped! Personally I think that you would like the Red Devil's! But you can decide on your own! After all, it isn't really up to me, is it? :):)