Good comparison between Roku and Chromecast here:
http://www.pcadvisor.co.uk/reviews/digital-home/3507480/google-chromecast-vs-roku-streaming-stick-comparison-review/
Browsing the web is on the whole unsatisfactory on a tv, smart or otherwise, for a number of reasons. You sit much further away from a tv than you do from a pc or laptop and that feels odd, to me anyway. You have no privacy because anyone else in the room can see the screen. The onscreen keyboard is clunky and awkward and the keyboard that comes with the tv is often slow and is yet another thing to lose down the side of the sofa.
I find it preferable to watch tv on my media pc than browse the web on a smart tv. Many people who have bought a smart tv don't really understand what they've bought and don't connect it to the internet.
My pc is a 24" all in one media pc and is perfect for the bedroom or spare room to use as a tv, tv recorder and pc. If you are thinking of replacing your main tv but there is nothing wrong with it, think about the Roku or Chromecast before you spend lots of money on a smart tv. They are both cheap enough to replace as the technology develops.
If you are looking for a smart tv as an additional tv, think about a media pc instead.