The two primary causes of canister leaks are inferior plastics used in some low-end canisters that will crack too easily and, much more commonly, insufficient or improper maintenance of the seals. The seals inside a canister need to be either lubricated or replaced on a regular basis. If you ignore them, your canister will develop leaks over time.
Having used so many different filtration methodologies over the years, I am no longer that passionate about there being a "best" one. HOB, canister, sponge, sump, etc they all work and all have their place.
For my own use, in display tanks I like canister filters
- They are quiet
- They minimize evaporation
- They have large amounts of media capicity
- You can large amounts of flow without the use of powerheads/pumps
- Most importantly, as @brendenscott points out, they let you get mess out of the tank and allow the use of in-line heaters
My personal preference as it relates to canisters is the Eheim Professional line or the Fluval FX line.
In QT tanks, I like HOB filters
- They are easy to clean
- They are inexpensive
- They are also easy/inexpensive to sterilize if you get something nasty in QT
- They provide good flow in a small tank and all the ones I use have some type of variable flow control
There are only three HOB filters I like right now. The Aquaclear, Fluval C and Seachem/Sicce Tidal line of filters. All three have media flexibility, flow control and they work. Right now I have switched out 100% to the Seachem Tidals because they self-prime. We have a lot of short power outages where I am and I have fried countless HOBs from them failing to restart after a 5 minute outage. That being said, they are a very new filter so reliability is highly unproven.
In fry tanks or back when I had rack setups I use/used sponge filters
- They are the cheapest option by far
- They pretty much never fail(the air pumps can fail, but not the filter itself)
- You can run a huge number of tanks off a single pump
- They have no moving parts
I prefer the sponge filters that stick on the back of the tank but have no particular brand loyalty as they are a pretty basic item.