Just follow the main guide of win2008workstation.com, step 10 about themes/aero should bring the most win7 looking experience I guess.
Server 2008 r2 can be a lot better but it depends mostly on what you’re gonna use it for. Server 2008 r2 has a lot more features compared to win7 but if you dont use them win7 might be better as server OSes tend to have a little more trouble with compatibility.
It’s widely preferred and used because, unlike R2, it’s readily available to consumers through retail and pre-installed on new computers. Also, unlike R2, it doesn’t need a fairly involved customisation process to turn it into a workstation.