Well with the 45 i would get a pair of gbr and a pair of apistogramas. Then get about ten neon tetras and three rainbows. And maybe a school of glass catfish.
I would have it heavily planted with t5 plant lights or whatever they are lol. A little rock cave for the GBR. Probably sand for substrate.
With the 55 i would get three discus and have it planted so that the plants only grow to about mid way up the tank and have it full of red cherry shrimp and ghost shrimp. I would also have about 7 corys.
Or
The 55 would have 3in of sand and i would get about 10 similis, multis, or whatever shell dweller you like. Then have a rock pile in each back corner and get 2-4 julis.