As I see it, the advantages of a sump are:
1. easier to maintain/clean than canister
2. heaters, return lines, thermometer, are no longer in the tank with the fish.
3. lower cost.
4. more permanent/reliable plumbing of drain and return lines.
5. versatility--easier to add more pump capacity to a sump than a canister.
If you agree with those 5 advantages of a sump over a canister, then you need a sump. If you disagree with those, or you can come up with some advantages of a canister, then go with canisters.
As for a wet/dry, that means what--water flows over a plate with holes and falls through a bunch of bio balls or a flows through a foam filter? I've never had one, but it seems to me like it'd not be easier to clean than a canister. As for better bacterial filtration with a wet/dry.........I don't know about that, so I didn't put it in my list of advantages for a sump. But, with a wet/dry, I still see 4 more clear advantages of a sump over a canister.
I will say this, though. I think that a sump is a better fit for a large tank for two reasons. Getting equipment out of a tank is very important in a large tank because, presumably, it will house 12-14 inch fish that can and do break thermometers, pull on hoses, etc. And the cost of a sump is not much less than the cost of a canister on smaller tanks. Enough canister filtration for a 300-500 gallon tank is what--$500 or $1000? I think you could build a sump and plumb it for $500 or $600. But what's the cost of canister filtration on a 140 Gallon--$200? I don't know if I could do a sump for $200. It just seems like sumps are only cheaper as the tank size gets big. Cost is probably a wash for a 140 Gallon.
