iPhone with extra battery pack. You get best of both worlds in terms to carry things around. The more you carry stuff around the more you tend to lose it.
Pretty much depends on what you actually need and how your lifestyle can fit into it. I need the MP3/movie/games/backoffice stuff/internet on wifi/normal phone (3G disabled, data roaming disabled) so it can sustain quite long when I'm working outside. When I'm inside I need 3G and Internet on the go so that pretty much suits me. I choose 32GB because my MP3 is nearly half of it plus 1GB of apps, nearly 1GB of documents etc plus extra space for movies.
See how your lifestyle is and try to pick the one that suit it.
Owh yeah...that was the reason why suddenly I got converted into iPhone user since they launched 3GS