I'm pretty happy with LDN, been using them for a year, without any serious issues.
Sometimes I think I'm the lucky one, but a lot of my friends are happy too. So I'd suggest trying them first. And then if things don't quite work out, move and try PTCL as well. But keep in mind PTCL customer service sucksors, and it sucksors big time.
PS. I'm on a 2 MB connection with LinkDotNet, and it's been working great 24/7. The last time I called their customer support was in February!