I've got 3 right now, which is probably excessive, but it's often useful to check one against the other, especially while I'm starting out testing every little mouse fart for its effect on my blood.
Accuchek Mobile - the most reliable, but also the most expensive to keep up. I only use it when I can source cheap cassettes from ebay.
Accuchek Performa - again, I use it when there's a deal on for strips. It's the fastest reader of the 3, the most convenient to use and carry. Reads marginally higher than the Accuchek Mobile, and will occasionally spazz out and give you a crazy high reading.
SD Codefree - has a habit of going wildly off-course with consistently high readings for half a day (checked against the other meters) but then coming back down to earth later on. Can't figure out what's skewing the results. This unit has the cheapest strips, but with so many false highs, it could be a false economy.