This is probably religion but I would steer clear of break barrels, especially second hand: they rely fundamentally on the barrel precisely lining up again each time. That seems unlikely to happen to me as the gun gets older. So I'd say go for an underlever.

Which one is more interesting. I love my Weihrach HW77K and the HW97 looks very nice, although I've never tried one. The TX200 I tried on Sunday seemed OK too (although far too fiddly for a leftie like me).

As others have already said the best thing to do is to try some. If you can pop along to a club. For example we've usually got several springer shooters at a Shepreth meet.