The LPN typically takes about a year, whereas the RN is a longer education (two to four years, depending on the program and pre-reqs). Many people go for the LPN first and then take a "bridge" program to become RNs. This works out better for finances for some people because they are only out of work for a year and their employers MAY pay for the additional schooling to become RNs. However, depending on where you are, LPN roles may be limited. Where I am most LPN jobs advertised seem to be in long-term care facilities or in doctor's offices. Again, this may be different where you are, as there are many places where LPNs still play a large role in hospitals, so that's something to investigate to see whether this will work for you.
Here are some more explanations of the roles:
LPNs
RNs