Well, I don't think I can get dinged for this since I'm not affiliated with any of these, but before I began doing my own dedicated hosting, I had used single, reseller, and even dedicated servers with the following:
SuperUser (I wouldn't recomend them though due to poor service).
Asside from Super User (whose plans and reliability server wise is great) - Host Dime and Burton Hosting both have excellent support (including telephone, ticket, email, forum, and IM), are very friendly as well as knowledgable.
Between the two, I'd have to say that Burton Hosting has far fewer outages/downtime issues that HostDime - but even HostDime's problems are few and far between.
As for UnifiedNet.net, I have not used them for their linux hosting, although their Windows based system is the only one that I've used and the server was extremly stable (atleast in my opinion for a Windows host). And, at least they used Plesk rather than Helm or Ensim (two control panels that I can't stand).
Hope some people find this positive review helpful.
smartin [at] nocturnalhosting.com