I used to have one bag, period...and was never very happy with it.
Nor am I happy with a stable of them. (Well, to be honest, I don't know if I am happy with that because I have not amassed so many.)
But I do like to change them out with the seasons, as Cathy (cciele) does.
And I haven't yet found my perfect one for any season.
i think, in the long run, my bag collection will have to be like my wardrobe -- medium sized, mostly neutral, with some pops of colour.
What I prefer for regular daytime use is a shopper bag -- a structured satchel with a zip top (not just magnets), space for my phone, etc., a key attachment. I like partitions but not if they flop around (as I have learned to my chagrin with my taupe Tiganello bag, which drives me mad -- its partitions always collapse on themselves if the bag is not stuffed absolutely full -- and then I can't find stuff. Meanwhile, I can't really stuff it full because what I'd like to carry to do that doesn't fit in it! Grrrr.
Eventually I would like to create a small winter and summer bag capsule -- one light neutral, one bright colour, and one dark neutral per season. Along with a clutch per season. I also have a couple of evening clutches and a small cross body that is cross seasonal as well.