Couple of things:
-3G is data connection via cellphone
-3G is "usually" slower than Internet wifi but that is not 100% true all the time. My 3G connection with Tmobile is slightly faster than my wifi Internet connection
-3G main use or advantage is for users that need connection all the time and when not at home
If you don't need connection all the time and you are going to use your Kindle at home most of the time, keep the wifi model and setup wifi internet at home.
A good and not so expensive wifi router is Linksys. They are not the best but good balance between features, easy to use and price. The Lynksys should work with your Kindle wifi.