Which affordable Pancake for E-PM1 ?

the 25mm is for four thirds -- different lens mount than micro four thirds. scratch that off your list (if you get the 4/3 - m4/3 adapter, you've negated the portability of a pancake, and spent too much money).

if you're not even considering the 20mm, your choice is easy -- get the 14mm. the 17mm is not bad, but the 14mm is newer, faster, smaller, nicer. FWIW.