You
should wait until you have received all your tax forms that are needed for the
year that you are filing your return. If you expect to be issued a 1099-R it must be reported on your return.
Trying
to file early and then ending up having to amend because you used
incorrect/incomplete information is counter-productive. If your return is
incorrect/incomplete you have to amend it. Amendments have to be mailed and it will take months for the IRS to process
your amended return.