There's a lot of very different types out there designed for different environments, the first thing you should do is stop and ask yourself:
- Where are you going to use these shoes?
- How much hiking and how much climbing are you realistically going to do in them?
Some shoes have more padding than others making them better for hiking distances in, but the more padding they have the worse they'll be for climbing in, don't underestimate this.
Pay close attention to the tread on many approach shoes, the majority of them aren't really ideal for UK conditions (i.e. wet grass and mud!), the ones with a purely dotted sole will have better grip on rock but they are an absolute horror on grass.
The Camp 4 is in my opinion the best all round approach shoe for use in most places in the UK, it climbs reasonably well, it's durable, comfortable to hike in and the tread is lugged deeply enough to provide stability on loose ground.
There's a pretty good round up with some pros/cons of the major players on the US site outdoorgearlab.com here:
http://www.outdoorgearlab.com/Approach-Shoe-Reviews/ratings