Buell's later bikes were reliable.
Some of the early ones were reliable.
I had a 99 M2, and it was fine. There was a recall on the gas tank hold down bolts, and I think one other thing, but the bike ran good and really didn't give me any problems. I actually rode with Eric Buell once on a group ride, and also met him a couple of times at other events.
He's fast, BTW!
I actually have a Royal Enfield C5 right now. That's the 500cc "Classic" that they just stopped making after about 65 years, and a couple of minor changes. Mine was made in 2012 when they were still at the old factory and a lot of stuff was done by hand, so for example, the pin striping on the side covers is hand painted.
Other than a dead battery, which is my fault - it's never given me any problems. Was using it to commute across the Bay Bridge off and on for about 2 years. Starts on second kick. Gets OK MPG. Good off the line.
Re: my new Kawasaki - RE quality not as good. The Kawasaki is perfect. Everything is literally beautiful, even when you look at it close. No imperfections of any kind.
The RE on the other hand, you can see machining marks, crappy welds, and that kind of stuff.
That being said, I think Royal Enfields are good quality from the perspective that if you take care of them, they are durable. I know in India, they are used when people go there and go on bike tours. I think the reason is that they are so primitive, and there's literally a million of them there, and a million people who can work on them!!!