Pretty subjective comments, but here goes.
Have both the Telex 50D (for about a year) and Lightspeed Zulu (about 2 months). Have regularly used both in a noisy turboprop. The 50D is definitely quieter the passive attenuation is excellent ANR on it is great. Lightspeed Zulu is quite noisy with ANR off, but ANR on is very good, not as quiet as the 50D, but very comfortable.
Comfort and weight wise, dont mind either of them, 50D's ear seals are nice and LS-Z's have lighter clamping force.
Gadgets wise, the Lightspeed is the best. Listening to music through the bluetooth interface while being able to get weather updates enroute. Phone works like it's a person on intercom next to you. People often ask where I am calling from as the background noise is very quiet.
Reliability wise, Telex's built very well. Very robust. Lightspeed, not as tough but seem strong enough. Had a broken cable on the LS making the ANR intermittent - it was quickly repaired under warranty. Telex's seem tougher overall.
These days I end up taking the LS's flying most of the time due to the features built in.
Pretty happy with both headsets overall. If only Telex had a bluetooth interface!..
