I don't think you will find another as strong as R ponticum. It is a thug, spreading to strangle entire hillsides, of its own accord. It even grows on pockets of clay in chalk areas, which are neither particularly damp nor acidic. So it is clearly a very unfussy and robust plant, albeit that it won't grow anywhere overtly alkaline.

R luteum is the only other rhodie to have become naturalised in Britain, so one might think that is an easy one, but it died in my garden, I couldn't make it damp and acidic enough for it. But I have kept few others alive, a couple are even thriving. Fwiw, the red one that does well for me is Elizabeth, but it is a small to medium sized one. The pink one that does (really) well for me is Christmas Cheer; but it flowers early (usually about March, but can be as early as November) and you need to fleece the flowers if a frost is threatened during flowering.

So it is apparent that to grow any other Rhododendron you will need to be able to give it the conditions it desires, or it can give up on you.

Perhaps you could tell us a bit more about where you live and what kind of a soil you have. A good trick, by the way, is to look into your neighbour's front gardens, and see what thrives with them.