I'm in the market for new noise-cancelling headphones, and I'm looking at Bose this time (had been using Sennheiser PXC 250). The current model is the QC 25, but I've read a few reviews that say it is inferior to their previous QC 15. Any opinions? I can still buy some QuietComfort 15s at a slightly lower price - not really a significant difference in cost, but if the newer model is not an improvement, I might just take the savings.