i would suggest the Apple iPhone 3G or 3GS.
i'm currently using an iPhone 3G and it still works like new even though it's already a year old. no "hang" issues found on most smart phones. internet browsing speed is top notch. it also has the capability to store/push your emails.
you may also want to consider the new Sony Ericsson Satio. never tried using one but it looks promising. i think it's much much better than the Xperia.