I use the Elmarit-M, which is a wonderful optic and extremely sharp at the maximum aperture. It's about the maximum in terms of size and weight that I'd consider for a travel lens (the Summicrons are significantly larger). The new Summarit-M is marginally smaller and lighter than the Elmarit-M, and reviewers all seem to opine that there's nothing between the two optically (although personally I'd miss the Elmarit's built-in hood).
The Elmar-C (or either of the Minolta versions) is a tiny little lens and very, very sharp – not quite up there with the Elmarit, but commendably close. I used to own one some years ago and it, with a 35mm 'cron and M6, made for a wonderfully compact high-quality travel kit (I sometimes think about picking up another one for that reason). Haven't tried the Hexanon but I've seen great results from them and owners seem to love 'em. Either would be a solid purchase.
There's also the modern and vintage collapsible Elmars to consider. I haven't tried the former, but the old one's are fabulously made (although surprisingly heavy), but quite soft.