Shoulder strap or backpack?

[blackcurrants]

Please will you help me decide between a Packabe and the Skip Hop Duo Deluxe? (Links to the US amazon as we live in America atm).
LO isn't even here yet, but for some reason this is niggling at me today. Preg hormones, perhaps?!

We live up 3 flights of stairs so I don't want something sliding off my shoulder as I try to lug a baby and pushchair up and down. I'm also hoping to use a moby/ergo for most of our walks around town (easier to manage with all the stairs, when walking the dog, etc) and I'm worried about the shoulder strap slippage then, too. Would a backpack be a better bet?

We're going to use cloth nappies (bambinex teddies, mainly) and I've heard that means we'll need a biggish bag, is that right?

Also I might well be commuting with this LO a bit, so being able to fit some of my stuff in as well would be a bonus.

Anyone had a backpack one and hated it? Anyone find a shoulder strap slips off their shoulders and irritates them?
Any thoughts?

I have a Baby Bjorn backpack with lots of room in in and find that quite useful, although it is now mainly my gym bag as I've invested in a Storksak, which I love. If you choose a bag with a strap, make sure it is long enough to fit across your body messenger-style so you'll have both hands free. BTW the Skip Hops haven't had amazing reviews - I coveted one for ages but after reading negative reviews I went for the Stork and haven't regretted it.

I have a Caboodle bag here I find it big enough to carry stuff for 2 los, they are now 3 and 4 and I am hoping it will last for dc3 due in July.

It can hang on the back of the buggy, and carrying it is really comfortable (even with bad back). Also dh is quite happy to carry it (some of the more 'decorative' changing bags are a bit ridiculous looking!)

ooh, thanks for the feedback on the Skip Hop, BarbaMamma - that's good to know. I'm now going to think about the Caboodle offerings, too, so thanks hazey - hearing it's comfy is key, plus I totally agree with you about the decorative thing. DH is going to carry this a lot, and while he's absolutely man enough to rock my handbags when I need him to carry them, neither of us are that into floral prints!

Hmm. Caboodle, and where I can get it in the USA... This is SO much better than actually, y'know, working ;)