Most of the Kossel variants are using jheads. They're cheap and
light, and can handle a variety of filament types. Lansing Makers
Network's had a really great experience with the magma hotend for
printing VERY fast with ABS, but it only does ABS.
If you get a j-head, buy it from
hotends.com, or a reseller that gets
their stock from hotends. Some of the chinese versions on ebay are of
spotty quality.
LMN's got a Rostock, a Kossel Mini in the mail, and a Wolfstock under
construction. We've run into most of the problems you can run into :)
Calibration is particularly fun on delta machines. Ask away if you
run into any problems.
--tim