Mostly just came here to bash the 739 like the others. My first DL flight of the year, this morning at 9AM (BOS-DTW-SEA) was delayed due to MX issues. BOS-DTW was on the A321 and DTW-SEA was on the 757 (dont recall if it was a 752 or 753). Had to reroute through ATL and sit around there for 3.5 hours. The worst part was having to switch from my favorite domestic bird, the 757, to my least favorite, the 739. And on a 5.5 hour transcon, no less! Thank god we were at least in paid FC originally and were able to rebook into the same. That flight would have been worse in MC or even C+.