Lots of good suggestions, and as I think you can see, which route is the best route probably depends to a large degree on your driving preferences. I lived in Marshall for 6 years, so I've tried variations on most of the above.
Going through Tyler affords you the most 4 lane roads, but Tyler will really slow you down.
I found going through Rusk, Alto, and Madisonville not to be a time-saving route (at least for my driving), and inferior roads to boot. If you do want to go that way, I think there is a farm road off US 79 outside New Summerfield that will get you there quicker than going all the way down to Mt. Enterprise to catch US 84. Again, it's largely personal preference.
I also try to avoid going through Madisonville, especially if you are approaching from the North. It is simply an unecessary, time consuming detour.
My suggestion would be to take US 59 to Marshall, and from there:
Texas 43 to Henderson.
US 79 to Buffalo.
79 is an OK road--the only problem being the trucks from the Wal-Mart distribution center outside Buffalo will slow you down.
From Buffalo, there are several options, two of which I would take, depending upon driving conditions (time of day, weather, traffic).
1. The backroads route:
US 79 from Buffalo to Jewett
FM 39 to North Zulch
Texas 21 to Bryan
Although it is a farm road, FM 39 is a great time saver with little traffic that, for the most part, runs along the Santa Fe RR tracks--meaning its fairly flat and has few curves. It is an alternative to I-45.
2. The interstate route
I-45 to OSR
OSR to Normangee
FM 39 to North Zulch
Texas 21 to Bryan
OSR is not a very good road, but it's only 10 miles from I-45 to Normangee. This saves you going through Madisonville, and also shaves about 5 or 6 miles off the trip. Taking this route is a few miles longer than going through Jewett, but you might make the time up by not being slowed by traffic (and a lower speed limit in town) in Jewett.