The Q-Tron was my very first filter. I went through a bunch after that (Dod FX25, Chunk 00Funk, Maxon AF9, MXR Bass Auto Q, Boss AW-2, Digitech BSW to name a few) and I now own a Musitronics Mutron. If you can get one for under £300, grab it - You won't regret it.
It's the fattest, greasiest, wettest filter but it's so musical too - Really hard to combine all those elements into a filter, but the Mutron passes with flying colours.