The 1MZ-FE V6 is actually very reliable. It is like any FWD V6 difficult to do maintenance on, but if you need a little extra power it is a decent option.
The 5S-FE is a very reliable engine as well, with the valve cover being one of the few places they commonly leak. This is a cheap and easy fix.
They are reliable, cheap and economical cars to run and repair compared to some on the market.
My only downside to them is the interior comfort is a little lacking, but you really can't expect much more at that price point.