What is the best way to delete all of a large table in t-sql?

We've run across a slightly odd situation. Basically there are two tables in one of our databases that are fed tons and tons of logging info we don't need or care about. Partially because of this we're running out of disk space. I'm trying to clean out the tables, but it's taking forever (there are still 57,000,000+ records after letting this run through the weekend... and that's just the first table!) Just using delete table is taking forever and eats up drive space (I believe because of the transaction log.) Right now I'm using a while loop to delete records X at a time, while playing around with X to determine what's actually fastest. For instance X=1000 takes 3 seconds, while X=100,000 takes 26 seconds... which doing the math is slightly faster. But the question is whether or not there is a better way? (Once this is done, going to run a SQL Agent job go clean the table out once a day... but need it cleared out first.)