I don't have any experience with internal filters, but I guess it makes sense to have one if you're doing a heavy planted tank because then you don't have the waterfall effect from the HOB breaking the surface and letting the CO2 out of the water.
You dont want an undergravel filter in a planted tank, the roots will grow thru the plates making it almost impossible to safely remove the plants without damaging them.
I used undergravel back in the early 80's with no known problems, but when I tore the tanks down it was a mess underneath the plates so now I would never use one.
beneficial bacteria lives on every surface of your tank regardless of type of filtration, regardless of the surface area you provide in a filter the bacteria load is only going to be as large as it needs to for the tank, if there isnt enough food for the bacteria it isnt going to survive. So the real question is how much surface area does the bacteria need to survive? If your water parameters are within the safe ranges then I would say you have sufficient surface area.
The HOB and canister are going to provide chemical (carbon bags), mechanical (filter floss) and biological (bacteria living on sponges, bio wheels, etc) where the only filtration the undergravel is going to provide is biological, some may argua that it provides mechanical because the gravel would act as floss or pads in the other 2 filters but due to the size of gravel alot of large waste will get thru it and settle on the bottom of the tank, where canisters and HOB's catch the waste on removable filter pads that can be changed or cleaned.
If you are using an HOB filter with a disposable cartridge bag that is prefilled will carbon do not wait for it to fall apart before changing it, if it falls apart it will dump the contents of the carbon bag into the tank and will suck some of it back into the filter and possibly damage the impeller. I know this from experience.
