Hello Socksarecool4!
Apos gave a pretty thorough rundown of the options out there, but if you are looking for an e-ink device, I too would definitely suggest the Sony DPT-S1. Writing on the device is usually a breeze! There may be one or two areas near the edge of the screen that are sometimes not as responsive, but it really is the best I have seen from an e-ink device. The 13.3 inch screen is also very nice to read on. The only problem is the price, although Sony recently heavily reduced it to $599 on amazon. There are other 13.3 models out there right now, but, sadly, from what I've heard I cannot recommend any of them (ex. their Lithium Polymer batteries developing bulges.....scary!).
They are also actually more expensive on average at the moment.
If only working with PDF documents is fine for you, then the DPT-S1 seems to still be king of the 13.3 inch e-reader hill.
A very close second is the Onyx Boox M96. They are harder to find nowadays, but its successor, the N96 is available. They have a smaller screen at 9.7 inches, but the newer model, the N96, comes in two models: one with dual touch (electromagnetic stylus+touchscreen) and one with a front light.
If you would like a better idea of how the Onyx Boox M96 fares against the Sony Digital Paper in terms of fluidity of writing and other factors, please see my video review of both together on you tube. Just type in "Sony Digital Paper v M96" and look for the video with my name as the author. You can also find the link to it in the Onyx Boox forum on here.
Hope that helps!