I have a Eureka upright as well. It's been fine, but it seems kinda cheaply made compared to an old Kirby I used to use. Of course, I hated that Kirby. The thing was all metal which made it quite heavy. The Eureka hasn't given me any problems in about 5 years, so I can't complain about it. One thing to really watch out for though is to make sure you get a really, really long power cord and possibly a long hose as well. My cord was fine for the apartment I bought it for, but not as good for the house.
Stairs are a mixed bag. If you have a really long hose or hose attachments, it really doesn't matter whether you get upright or canister. I used to own a canister and hated lugging it along doing the stairs, but now I'm finding it was much, much easier than using the upright with a short hose.
I haven't used a bagless, but I can't see the benefit. So I vacuum stuff into a canister, then when I empty the canister all the dust flys everywhere? Doesn't sound good to me.