Here is the lowdown on all the different varieties of T-Gel:
Theraputic ('Normal') T-Gel contains .5% Coal Tar, the active ingredient. Then there is T-Gel Intensive Anti-Flake which contains, I believe, 1% Coal Tar. Same strategy, more chemical. There is also another variety of T-Gel the specific name I forget but it is something to the effect of 'anti-itch'. It contains .5% Coal Tar, and also contains Menthol which is a mild topical anesthetic and feels good on the scalp. Then, there is T-Sal, which does not have Coal Tar, but has Salycilic Acid as its active ingredient. T-Sal also comes in normal and enhanced strength.
Coal Tar is an antifungal, which helps keep in check naturally occurring fungi on the scalp that can cause itching and flaking. Salycilic Acid is an exfoliant. Both are two methods of attack against the same basic problem. I would start with T-Gel Theraputic and see how it works, then you can meander to any of the other products depending on the results you get from it.