From Beltway 8 and I 10 on the west side of Houston, on a Friday afternoon around 5pm or so, am I better off taking the beltway to I 45 all the way up (does 45 have a good HOV lane?) or taking 290/6 to Waco and 35 the rest of the way?
HOV's not bad. I just took it that way a couple of weeks ago at that exact time of day. The hardest part is finding where to get on. Make sure you've got that straight because you can't just drive to the area and follow the signs. They are seriously screwed.
I'd take beltway 8 north to hardy tollroad and then funnel into 45 north.
DO NOT take the 45 N exit off beltway 8, the hardy tollroad will spit you onto 45N a lot faster. traffic will be thick until you get past the woodlands mall, it'll open up some right before conroe and then you'll start moving.
stop at woody's smokehouse in centerville. they got some good eats there.
If you can do that, you may as well work your way over to the Hardy Toll Road and take that all the way until it ends. On the same note, I agree about leaving earlier, if possible.