I would go for the most recent version of the game you can find, as it may not require patching that way. Beware RTW Gold in that some pressings of it shipped with RTW at 1.5, but BI at only 1.4. Installing BI would then roll back RTW to version 1.3, making it necessary for you to patch both back up to 1.5 and 1.6 respectively. I have one of those copies, and it sure came as surprise to me.

You might want to look at Total War Eras as well. It comes with RTW and all the expansions, as well as MTW and STW and all their expansions as well. They are all at the highest version levels so no patching for any is needed. They also ship in dvds, so you do not have to sit there change out multiple cds when you install them.