i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol



performance wise are they in the ball park, does one have a clear adv
over the other in a particular circumstance??

Check out the last bit of this page:

http://www.cebik.com/vhf/gh3.html

It's got the sort of comparison you're looking for...