Fun shopping, isn't it?
If you go with one penquin, I'd go with the 150 or 200. The larger 200 does allow for more filter medium options. I have no experience with the nano canister, but it looks pretty cool. I'd love to know how quiet they are...most of the larger canisters are darn quiet. The hang on back filters (like the penquin or aquaclear) are also quiet as long as you keep the water level high enough to reduce the waterfall like noise.
The canister may provide you with greater water output options (meaning how/where the water stream is directed into the tank) versus a hang on back filter, which essentially is going to push water across the top from back to front.
Given you're looking at a 20 long (not sure how tall they are), the stealth heater will likely need to go in horizontally (it's 10" long)...not a big deal, just a little less convenient to adjust and another cord running up the inside of the tank..but I still think it's your best choice.
If you go with one penquin, I'd go with the 150 or 200. The larger 200 does allow for more filter medium options. I have no experience with the nano canister, but it looks pretty cool. I'd love to know how quiet they are...most of the larger canisters are darn quiet. The hang on back filters (like the penquin or aquaclear) are also quiet as long as you keep the water level high enough to reduce the waterfall like noise.
The canister may provide you with greater water output options (meaning how/where the water stream is directed into the tank) versus a hang on back filter, which essentially is going to push water across the top from back to front.
Given you're looking at a 20 long (not sure how tall they are), the stealth heater will likely need to go in horizontally (it's 10" long)...not a big deal, just a little less convenient to adjust and another cord running up the inside of the tank..but I still think it's your best choice.