The traditional handles are great, especially if you're using them at home, but, if they're going to get rattled round in a travelling toolbox, then the retractable ones will stay sharp much longer - and it's a lot safer rummaging round if the blades aren't exposed.
If you speak nicely to a nurse, they might be persuaded to let you have some stitch cutters - they can be useful in awkward places.
There is also the Veritas scalpel handle, which uses a collet arrangement that will take most of the various blade fittings. The cap in the handle has a strong magnet and will hold around six blades of various shapes.