If you haven't tried buckling spring before, get the ubiquitous model m with the familiar 101 layout. You can get one new from Unicomp or there's always many originals available on ebay in various states and prices. Once you have a feel for the M, you'll be able to decide if you really need an M.
And if you do decide to move into an F and love it, you really need to consider the F-122 for the mother of all keyboards on your desk.