I have three compacts, all external bearing:
-Truvativ Elita
-Shimano R700
-FSA Energy Mega EXO
The lightest and most durable
in my experience is the FSA Energy Mega EXO (787g w/BB weighed on my scale). Truvativ rings (at least the Elita) are just crap; I broke a tooth after a few hundred miles. Shimano R700 rings are too soft and show far more wear than the FSA Energy and it's not even a year old. The R700 has far less miles on it.
FSA Energy Mega EXO gets my vote....$198 from Reporto Corse. I got mine when they were $126