Ray,
Welcome to the forums! Please note the date of the thread you "re-opened". It's 5 years old. You may have better response by opening a "new" thread.
If you car is under 3,000 lbs., it is genrally accepted, that with a higher revving engine like a 355 or 377, the 'glide is a better choice. For 1/8 mile cars with stiff gearing, also, 'glide.
For a heavier car or a lower revving engine (under 7,500 like the 400SB), TH350 would have an advantage, because of the gearing you "heard" about. 1st gear is much "deeper", providing the needed torque multiplication on "launch".
A "stock" PowerGlide is okay, not GREAT. It can be "beefed up". The case is generally fine. The internals need to be upgraded if you're going to use big HP or a power "adder" (nitrous, etc.).
Same thing for TH350.
If this is to be a SERIOUS race effort (attacking the points, going as quick as possible, etc.), due to the added torque output of the 400, I would recommend TH400 over ALL the others. Far tougher than any other auto (stockish), and good gearing, TH400 has another advantage not usually understood. When most auto transmissions "shift", one portion is "applied" and another "released". This takes 2 separate "events" in the trans. With TH400, nothing ever has to be "released" once it's in 1st. It simply "applies", "applies". You can demonstrate that to yourself next time you're at the track. Find a car with a TH350. Find another with TH400. Pay close attention to them as they shift "down track". There will be a slight rasing of engine speed when the TH350 shifts. When the TH400 shifts, the engine will simply "change pitch". And don't worry about the parasitic loss (uses more power to "drive" it than TH350). It's true, but not as pronounced as the mythology, and with a 400SB, you have much more torque than smaller-cube small blocks. Those guys snag torque ANYWHERE they can find it, as that's the main "weakness" of small blocks, low-end torque production while still making power 'up high". Not the case with the 400...l
Jim