I use the Drinksafe Supalite bag system, it's been a really useful purchase so far. I had some issues with it on a trip earlier in the year but since stripped it down and given it some TLC and it's working as new again. It could've been the auto shutdown feature doing what it's supposed to do, I need to read up on that one day. The flow rate isn't as quick as some of the other options but it's great for hanging up around a fixed camp for a few days. There were some questions with the filtration level on the filter originally but I think it's been improved, I've never had any problems using it for cooking or drinking. It'll remove most nasties but no good for viruses or chemicals I don't think.
Rolls up to a decent size and weighs around 240-250g all in.
For fast filtering on the move I use a MSR Hyperflow, insanely quick with the same filter level as the Drinksafe. A small package and also weighing around 240g from memory.