You cannot count on being able to use 3G for anything but getting books outside the country your Kindle "belong" to (is meant to work in). Discussed in another topic here (and probably other topics as well, but stumbled upon this one when searching)
https://www.mobileread.com/forums/sho...d.php?t=117547
Personally I would go for the 3G anyway though. Like someone else said: Better to have it and not need it than the other way around!