Hmmm...that is a tough one. Colfax is a direct shot and isn't as congested as 6th Ave but by no means is it clear sailing either. If you are in south Lakewood, try 285 to Santa Fe Drive, however, it will often be bumper to bumper as well. I guess the best thing to do is to buy a coffee, turn on some music, sit back, try to relax and wave to me as we all struggle through the joys of traffic!
8 minutes from 1st and Carr to Colfax and Broadway, if there's no traffic (and you drive like I do). I timed it many times. One of the best things about living in Lakewood -- you get suburban atmosphere and real estate prices, but easy downtown access!
If there IS traffic, 14th Ave is another good route. It's just one block south of Colfax, and it tends to move quicker during rush hour. You have to jump up to Colfax when you get to Federal, but it buys you a few miles of smoother sailing.
This depends on the time of day you are driving. Highway 6 is the best and most convenient rout to get from Lakewood to downtown Denver, however, like most highways rush hour can be a beast. During times when you can drive the speed limit, it will take you about 15 minutes.