Might be too casual for you, but my standard travel purse is a leSportsac - either the day bag or ...crap I cannot remember [ok, looked up - Deluxe Everyday Bag and my new leopard print is the crossbody messenger - but it's not very big. I also randomly have a convertible backpack]. But it's a shoulder bag with a long enough (adjustable) strap I can make it crossbody. Which I do. Their crossbody bags are too small for me (I have one but I almost never use it). My dream purse is the out-of-production Tumi Sumatra -the current Tumi bags aren't appealing to me.
(I also have nylon bags from ebags, travelon, haiku, timbuk2.....It's not that I have a bag problem. It's that I never get rid of anything ;-) Not bags that will always "fit"!
I was looking for new bags over the summer - lots of advice here! I pinned an older Kate Spade leopard print nylon (never came in to The Real Real - I found the lesportsac by accident when I was looking for nylon leopard print!) And some MZ Wallace - I know many people love them, they seem so expensive to me! But I have a few I've been looking at on TRR or checking during a Nordstrom sale etc.