I know there are many different scenarios, however, I was just wondering what is the most common size weight used for a regular T-rig worm?  My guess would be 3/8 oz?

For me, there is no regular, weight depends on conditions..i.e..shallow and calm, 1/8 oz..wind and deep, I'll toss a 1/2 oz..If I have a 10" ragetail anaconda, I'll use a lighter weight. If I'm fishing from shore, and need to cast further to get to a spot that I think will produce, I'll use a heavier bullet..But, I try to use the lightest weight I can.

Man, so much goes into this that it is hard to say! Lure/hook size, wind, fishes mood, cover, line/size. Let the fish tell you what they want. If you can get away with weightless, start there. If the fish are active you may need a bigger weight to trigger them. My most common rig when pitching to scattered cover is an 8" ribbon tail worm, 4/0 EWG hook, 17lb fluoro and a 3/16 oz Tungsten weight.

1/8.

3/16

¼  

when fishign a 7 inch worm shallo 1/16 ounce and when im fishing a 10, or 12 inch worm shallow 3/16 ounce.when I fish deeper I will add more weight, but I think a slow fall is extremley important.

if you just had one weight to use for everything...i would say  1/4 oz would probably be the most versatile...good at most depths

1/16 to 3/8 for me.

always unpegged.

I use a 1/16th with a standard ribbontail worm.  It seems to give a slower drop rate than the 1/4 oz weights and I'm not trying to drop my bait through vegetation.  I like to work the worm just over the tops of sunken brush and the light weight lets me work it slower with a more natural drop rate.

¼

1/4 oz covers most presentations.

8-)

I always try to use as little amount of weight as possible. I use heavy weights in deep water or I peg the weights in heavy cover. Usually in deep water though, I use a carolina rig. Texas rigs are best in shallow areas.