Neither.
Ok, the TB display is good but, unless you find a really good price used, it’s too expensive. $300 is too much unless you really, really need it to match the look of your iMac. If that’s your primary goal, stop reading now.
A modern HDMI backlit LCD is as bright and has a great picture, uses far less energy and runs cool to the touch. It can be had for le$$ new than a used Apple monitor. In addition, LG makes 27” 4K monitors that can be had for $400 or so — far better than the Apple.
I forget if the 2013 has an HDMI port or not. It’s no big deal if not.
To hook up any HDMI monitor to a TB or Mini DVI port on a Mac, you will need an inexpensive Mini DVI port to HDMI adapter. $6–$10 on Amazon. Most new monitors will include the HDMI cable.