Was in the same situation myself a few years ago, and after consulting here whent with Clook
Have a reseller account plus a dedicated server with them now. Reseller account has probably had 99.999% uptime over the last 2 years. Only downtime I can remember was when they moved to a new building.
Clook answers tickets in minutes rather than hours or day which is a big bonus.
PHP5 - yes
Migrating - if your current site uses CPanel it is very easy to migrate. We moved from Fasthosts which didn't use CPanel, but was just a case of downloading the web files and uploading, and dumping the MySQL data and uploading it.
As Clook says - a dedicated server is not a replacement for reseller hosting - something which I agree. The dedicated server hosts a message board that is very heavy on "Server Load", so this dictates the dedicated bit. Any host would quickly eject it from a shared server account. With a reseller account the server you sit on is fully "managed" at no extra cost.
Clook Internet Ltd, UK based web hosting