I own five powermeters now...The first three were SRMs of various generations. They were all fine...until the battery needs to be replaced which even if you overnight the crankset to SRM will take them 2 weeks to change (why???). My last two powermeters have been Shimano and they're great. A little slower to register jumps in power, but great quality and best of all they're rechargeable!
The customer service at SRM was so bad (slow, unconcerned that you're without a bike while they drag their feet) that the last time I sent one in, I sent it in the Shimano box as a way of letting them know they had some competition. The Shimano is less than half the price too. I couldn't be happier!