Don't you have a Samyang 50 f/1.4, why not just take that? It's a reasonable size and weight.
If that isn't an option and the only choice is those 3 personally I would go with the Samyang 45mm. The Sony 50mm has quite slow a.f and the 55mm while being nice and small and also being quite sharp for me doesn't have nice rendering and colours can also be a little bit meh, a.f is quick and reliable though. Samyang 45mm is decent if you get a good copy. 55mm might also be a bit long if its the only lens you bring.
50mm wouldn't be my choice for travel and holidays, if it was me I would probably be wanting a 35mm, if you are looking for a one lens type thing.