I have a second generation Chromecast on an old TV that only does 1080p. I'm fine with that, I don't care about the resolution. Someone told me that I might like the new one with Google TV, but I don't know much about it. I pretty much just cast from apps on my phone, so I'm not sure if there's any reason to upgrade. The only thing I don't like is sometimes the Chromecast icon doesn't show up and I have to restart the app, but I doubt that's on the Chromecast end.
Overall, I'm pretty satisfied with what I have, but I've been looking at comparison websites and they aren't really telling me what I need to know, which is if I'm missing something good I shouldn't be missing.
Also, this is not really important, but I'm on Chrome and Google thinks "Chromecast" is a misspelling.
I'm curious about the next gen chromecast as well. I heard/read that it could manage h265 content as well as it having google tv which you can use for IPtv.