Difference between Horimiya 2012 and 2021.

If you start watching Horimiya I will suggest you to watch 2021.  Because of the following reasons: 

2021 adapts the manga

The OVAs adapt the web comic

It’s the same author, same story, same characters, different art style, different format. I’ve heard that the web comic is also different in tone & darker. I haven’t read the web comic but have seen the OVAs. It’s basically what the 2021 anime would adapt & the OVAs currently stops at if I remember correctly 

If you’re also wondering do you need to watch the OVAs, I feel there’s no need to. At least not until you finish this 2021 adaption if not you would just be watching repeated content at some point. It’s going to be more or less the same content in this adaptation. But if you’re a fan it’s just more welcomed content, also the OVAs coming in May are not 2021 anime’s OVA but continuation of the Hori-san to Miyamura-kun OVAs :)

Still you want to see the difference first watch the 2021 and they start watching 2012 you will found out it is same just tone and animation are good in 2021.