If this is a discus only tank then I would say a nice L-14 because they can take the temp and will eat almost anything.
I have a pair of L75's in a planted 90 community tank with only 1 discus. they are really peaceful to small fish but PC says they can reach 10"
The L75's don't go up on the glass very often and are not algae eaters per say. they are almost always out during the daytime especially if there is any food. They do uproot what they don't like which in my case is the spiral val's but they seem the leave the rest alone. the spiral val was quite thick so that could have something to do with it. ie. they have created paths through the forest