I have a Tomy carrier for my eldest dd, we used it twice and I never used it again, it was awful to get the baby in and out of, and my back just couldn't take the strain. (and my eldest was a premie and a very small baby)
DD2 was a BIG baby, she was 9lbs 4 born and just got bigger and bigger! A friend gave me her Baby Bjorn and it was a godsend - the design is such that is is very very easy to get the baby in and out even by yourself, and if the baby falls asleep you can just unclip it and lie her down without waking her (that's worth a lot of ££ right there!) I carried my baby in it for at least 6 months (she was probably 20lbs), maybe slightly longer, and I have a pretty weak back. I think if I'd had the Active version we would have used it even longer. I think it's a brilliant carrier and wouldn't consider a different model to be honest.
I also used a sling similiar to a maya pouch, which I thought was fab for around teh house, but it put all the weight on one shoulder and I couldn't walk for long with dd in it (maybe 20 min max), but I could carry her for a few hours in the Baby Bjorn.
the sling's big selling point, was that my baby could lie fairly flat and sleep in it, while I sat at the pc, or at my desk, or even ate my dinner, and I had both hands free, and she was basically held across my lap - the baby bjorn puts the baby in a more vertical position and it would be harder to eat for example while she was in this. Since DD wanted to be held pretty much 24/7 for the first 3 months, the sling was also very useful!
Bev