There's a (dumb) debate over what "4G" is, but frankly -- iPhone doesn't have it. iPad on Verizon does. (LTE) AT&T's "4G" isn't up to par.
I'd go with the Samsung if you want the best performance (today).
iPhone 5 will probably change all that fairly soon. When, is anyone's guess, but manufacturers are saying they're starting to ship individual components.
This from a dyed in the wool Apple fan for most stuff.
As a side-note, iPad "3" / "New iPad" has LTE on Verizon available today, and it smokes anything else running iOS -- if VZ/LTE is available in a particular area.
I was seeing 20M download speeds lying in my TENT at Oshkosh on Verizon's network there.
Ipad "3" on Verizon also can create a free WiFi Hotspot for up to 5 devices that uses whatever data plan data you have for it.