Modern smart phones generally fall into one of four categories:
The problem is that mobile phones are a very personal item and judgement is very subjective (although Blackberry, once the leader in Business email can probably be discounted).
All these phones connect to business (and personal) email although (ironically) Windows phones connect to less Microsoft systems
than the others.
Before buying your phone(s) ask yourself a few questions:
What screen size do you want? Larger screens are easier to read but more cumbersome to carry.
What (apart from making telephone calls) do you want to use it for? Music, photography, Internet Browsing?
Different phones have different speakers, camera features, data transfer methods. Check the bits you are interested in.
Where are you going to use your phone? The national coverage is pretty good these days but by no means uniform.
Check with your service provider.
Lastly, don't forget to buy a case suitable for the environment in which the phone is going to be used.