depends on how you plan to use it.
if you plan to carry it a lot, a lighter laptop is what you need. in that
case Thinkpad 13 wins because it is over 1 lb lighter.
Tp13 also has more ports (with OneLink+), so it is easier to extend (for
more displays and devices). but it has a smaller screen, no touch screen,
and can not be used in a tablet manner. if you plan to use touch screen or
tablet way a lot, you may have to go for flex 4.