I flew Delta for the first time this year, and everything went great. BUT - chiming in with a lot of PPs - delays can happen with any airline. I watched my Delta flights every day for months before my trip, and my departure flight from home was rarely delayed/late - but when it was, it was LATE by 3+ hours, connections missed, etc., so I knew it could happen.
You want to talk about a lousy airline, though (oops, here I go again) - don't ever take American Eagle in and out of Dallas. Delay - delay - cancel - delay, switch gates 4 or 5 times (no exageration) - coming home from WDW in 2015, I ended up spending a night in Dallas because of cancellations and delays. There was also one day, several years ago, when an hour-and-a-half flight on AE to Dallas ended up taking about 9 hours, with a cancellation, rebook, and a pit stop for gas in Wichita Falls because weather was keeping us out of DFW and we didn't have enough fuel to wait. Whenever I fly them, I seem to end up with at least some sort of delay/change, even if it doesn't mess me up (I've made a couple of really tight connections in Dallas because of them). I think they really do have a pretty poor record.
Unfortunately, some of us don't have a lot of airline options. Delta is far and away my best option to MCO (times, connections - lots of options from ATL-MCO if I miss a connection - and flying their own proper jets to/from my home airport instead of the American Eagle/United Express commuter subsidiaries. Sadly, SW here is SO limited in service, it's not even a realistic option. So, for now, I'm sticking with Delta to MCO. But next trip is winter, and I'll probably be the unlucky one then.