Like Jason above, I have a Oase Thermo Biofilter; the 600 in my case, on an Aquael 240 litre tank. Like him, I find it very convenient, keeping the heater out of the tank, and its prefilter works very well.
Having said that, the other two main makes, Eheim and Fluval, have produced excellent canisters for years. My experiences with those 2 makes, and with Tetratec, have been very positive. In addition, Aquael are a highly-regarded aquatics firm on the continent (they're Polish in origin), so you are spoilt for choice! If you're new to fishkeeping, and you have a reliable local shop, it's worth spending the extra to buy via them, so they can advise you on setting it up.