Is it good for performance to sleep a Mac rather than shut it down?
A long uptime is four days? My MBP has uptimes of weeks. Not as snappy? I guess you're running out of memory or something else is wrong. 

I've never had this issue where the machine is not as responsive after closing the lid as opposed to rebooting. I generally only reboot because of WiFi connection problems or software updates.

To answer your question - just close the lid. Only reboot when necessary.
When closing the lid it goes into a sleep state which I think is very nice because when you open the lid it is almost instantly awake and ready to be used. While if you power it off it will take some moments to be booted.

You could leave the lid open as well if you like. The fist thing that is probably is gonna fail is the battery. To keep that in good condition make sure you keep your battery charged (there are other topics about this how to do this and what is the best).

In the end, the machine is built to be used and you should just enjoy using it without thinking to much about what is best. Apple already has that done for you :).