It depends on what type of scaping you are going with, in my opinion. I'll break down my thoughts below:
1) IM Nuvo Fusion 10
- smaller tank - bigger fluctuations in parameters
- cube tank - may be harder to find nice rocks/ driftwood pieces that are interesting, less plants can be planted in this space unless you get crafty
- the components, as you mentioned, are hidden which is a plus if you don't like to see them
- likely will fit on a table you currently have if you don't have a stand
2) IM Nuvo Black 20
- larger tank - less fluctuations in temp/ parameters (tell me about it with my 5gals... -____-)
- rectangular tank - easier to find and scale driftwood and rocks to fit the space nicely, more planting space if you like having large plant variety, more fauna options/ community tank option
- back is painted black already if you like the clean look, but no compartment to hide equipment --> however, it isn't terribly hard to hide your equipment behind tall stems or other taller growing plants/ it's easier to hide clear or black cords against black background instead of clear backgrounds
- heavier, so you may need a dedicated stand for this work of art!
- you might have to submerge your arm more to get things placed right, maintenance on plants and moving things around will be more difficult I'd imagine
I think with bigger tanks having more options, going with a bigger tank makes sense - you can hide the equipment behind bunches of stems, tall pieces or wood, or tall rocks. However, if you are going for something more for your own personal enjoyment, I'd suggest a smaller tank. I live in a studio apartment and I have 4 nano tanks ranging from 1gal to 10gal and having a collection of smaller tanks that I can enjoy allows for me to keep a wider range of fish that are incompatible with each other and scape the tanks all to their specific needs. If in the future, you think you will want to have a larger tank, I'd just go for the bigger one - you said they cost about the same price. Or you can get multiple tank syndrome and be like me with a bunch of smaller tanks
. Just note that if you are planning to get fauna, certain fish species that grow particularly large, needs lots of lateral room to swim (sorry cube aquariums), or school in particularly large groups will need that 20 gal to feel comfortable and safe. If you're doing just plants, light and the distance of the light to each plant will be the most important factor in choosing your aquarium.
-suggestions for hiding aquarium equipment-
- make a moss wall in the back
- use a tall rock or a group of rocks in an aesthetically pleasing way
(easier said than done) - use them to make mini planters to put plants that will grow to cover the air tubes, etc.
- get a piece of driftwood that will reach to toward the top and grow moss on it, or maybe the branch is a thick one
- use air tube suction cup holders to strategically run all your cables to the side of the tank and straight up to reduce the clutter (I do this on the back glass of my unpainted aquariums)
- grow some tall plants in the back - that's what background plants are for!
- get a custom fake 3D background that automatically has space for your equipment to hide as it is hollow