We're fortunate to have a fantastic pmUA crew base here in Seattle. They tend to be more experienced, and I'm yet to come across a bad crew. They always take the time to learn my name, and often tell me a bit about themselves. One grew up down the street from me, another told me stories about his grandchildren. I have complete confidence that they could handle any emergency with poise and and competence.
The other bases are much bigger and therefore a mix. The Chicago crews are generally okay, but I've had only a few positive experiences with Dulles-based crews. They're unimpressive regardless of age.
Newark is a big mix: the Portuguese, Hebrew, and some of the some of the German and French speakers are phenomenal. But the worst experiences I've had with pmCO crews are Newark international (NTA) crews working long domestic flights. They are bored, unkempt, and take little--if any--interest in safety. They duck behind curtains, flashing their "Ex-Con" bracelets.
I also think those "NTA" crews are just exhausted. The trips are "turns" (i.e. Newark-San Francisco and right back to San Francisco.) pmUA doesn't do this. The crews on these turns are tired, and their fatigue affects their personalities and attention to their job responsibilities. I assume those trips probably fly very senior (lots of productive hours and you sleep in your own bed when it's over.)
The Newark domestic crews are often better than their international coworkers, (aside from many of the "Speakers.") There are still some awful ones in that crowd, but most of them seem to be more committed to their jobs, perhaps less frustrated by the merger because they weren't with Continental for as long. Perhaps they're more adaptable.
Houston is generally a bit cheerier. Too bad Houston-Paris is gone, because the French speakers out of Houston were some of the best in the system.
I was starting to think that pmUA crews were better across the board (and I'm legacy Continental.) But I just took two short pmCO flights with terrific, fairly young crews. One was pmCO based in Chicago (I didn't know they had that yet); the others came from Newark and Houston. They were immaculately dressed, smiling, attentive, and seemed sincere, kind, and responsible. Also, one woman with an African accent was spectacularly good looking. A lot of US-based flight attendants can look really schlubby... this woman was definitely an exception!
The darkest side of the system is ExpressJet. Perhaps its the misery of the Jungle Jet, but the worst flight attendants have all been on ERJ-135/145 aircraft out of Cleveland and Newark. Two stick out in my mind as unthinkably rude. I wouldn't trust them in a second to help in an emergency. I just flew with two great flight attendants on SkyWest, so maybe their knowledge and skills will eventually make their way into the ExpressJet ranks.
What about foreign carriers?
It's a mix. If you think that European carriers are better, remember Sabena. I also thought the crew on Finnair were like robots, especially in comparison with their fantastically cheerful and inviting neighbors at SAS.
For me, I like crew members who are competent, friendly, attentive, pay attention to safety details, and who make friendly conversation when there is an opportunity. I've certainly enjoyed this multiple times on Air France, El Al, Air New Zealand, Aerolíneas Argentinas, and SAS. These carriers are big, small, profitable, bankrupt, with and without labor problems... it didn't seem to affect how they treated their passengers.
I have no doubt that many United flight attendants can provide high-quality service with an ongoing commitment to safety. But the airline is huge, divided, and in transition. Perhaps there will be some retirements, maybe inflight management will crack down on some of the lousier crew members (many people want their jobs), and we will see some improvement over the next few years. Fingers crossed.