Respectfully, it's difficult to get useful, actionable information for such a broad question (for many reasons). For example, I think these days, most airlines are pretty much the same: large corporations that try (to some extent) to provide a decent if basic level of service to customers. But as in all giant corporations, most employees are constrained in how far they can go to help, you will catch some people who are having good days and bad days, and often the things that make the biggest difference are beyond anyone's control. This summer we heard about (and some of us experienced) awful melt-downs at crowded airports, etc. When stuff like that happens, it tests any company's customer service chops. Also, people tend to remember and report (online) only when things go badly, not when things went smoothly. So you need to take reports with a grain of salt.
All that said, the old saw that "you get what you pay for" often holds true. Flying on a discount "low cost carrier", then expect low cost customer service and no frills.
As for specific airlines, many people have had good and bad experiences, which may not be a good predictor of what your experience will be. For flights to Prague, your options will be determined (to a large degree) on where you are starting from -- very different advice if you fly out of New York versus, say, Reno.
In any case, I'd focus mostly/first on the long-haul trans-atlantic flight because that's the one where you'll be spending most of your time. The relatively short hop(s) at the beginning (domestic North American connection to get to the trans-atlantic flight, if needed) and/or the hop from the airport you land at in Europe onward to Prague, those short hops are, well, short, and as long as the get you there, they matter less.
Most people choose flights based on just one consideration: the lowest possible cost. Personally, my comfort and convenience matters. I don't want a tiny seat (especially on the long flight), I don't want multiple long layovers (I also don't want too-short a connection, because things can and do go sideways with connections). All of those things are easy for you to see on the internet (for me, I start with the routing, then look at the specific aircraft type on that flight on that day, to check seat dimensions).
On-time records are easily found while investigating flights (most major airlines will show you the flight's on-time stats when you look at a specific flight).
In terms of what service levels to expect, it's hard to predict, other than the cheaper the ticket, there's a greater chance of minimal service (but there are exceptions).
In my experience, of the major US airlines, United has generally been good. Delta has generally been good. American has been spotty. European airlines can be good or bad, just like US carriers. It's really hard to generaize.
It would help others give suggestions if you specify where you are coming from, and where you want to fly to (if you have a specific destination other than Prague).
Hope that helps.