Whats bestpratice TTL for hightraffic www sites? Should there be a high TTL to make dnsservers around cache longer so the dnsserver wont have to get requests to often?
I can't tell you what TTL value to set, you can set it quite high (let say 1 day) but take care that if a day you need to do a maintenance and want to switch the resolution to a new IP . Until the TTL expire you may have request on the old IP. In some case it is OK because both IP will still work, in some case the old IP is not available after maintenance. In this last case you will probably want to decrease the TTL value before you maintenance to reduce the downtime for users.
So take care of this, if you think you could have to reduce TTL someday your dns server need to be able to enough powerful to handle that.