I'm somewhat unfamiliar with what the phone selection looks like in the UK, but here in the US, we're getting flooded with a wide variety of Android handsets, particularly those that are coming from HTC and Samsung.
I'm currently running the Samsung Epic 4G, which is based on the Galaxy S line of phones from last year. The main difference here is that I have a sliding keyboard, an AMOLED screen, and a 4G band radio (WiMax) to keep the internet speeds similar to what I have at home. My biggest complaint for the phone is generally the same as what most people have for the Samsung-branded Android handsets... Their UI is hit and miss (a little too similar to the iPhone), and often runs the phone down. That, and Samsung takes their sweet ass time when they roll out updates for their phones. Android 2.2 took nearly nine months to be added to the Galaxy S, and the 2.3 updates are just beginning to trickle out... But not to everyone.
Based on what we have here in the states, your best overall option is probably going to be the Samsung Nexus S, as it is the most up-to-date and "pure" Android experience that you're going to have. It being the second generation Google-branded phone, it will get the updates before any other handsets, and has the hardware to be a class-leading phone for a year or so. The only problem is that the Galaxy 2 is on the horizon, and that thing is a damn monster. Despite Samsung's limitations, they know how to jump ahead of the competition when it comes to hardware.