Which is warmer for fall and winter?

The Pro Club. Its 6.5 oz heavyweight cotton is noticeably thicker than the OG's midweight jersey.

Which one shrinks less?

The OG. It gets a pre-shrunk wash. The Pro Club's solid cotton colors can shrink, so wash cold and tumble dry low.

Which fits bigger and boxier?

The OG has a boxier cut with slightly dropped shoulders. The Pro Club is a regular relaxed fit, and it offers tall sizes the OG does not.

Is the OG worth stepping up to over the Pro Club?

If softness, a chest pocket and a logo matter more than warmth and size range, yes. For a thick everyday layer in extended sizes, the Pro Club is the better pick.

Which holds its shape longer?

The Pro Club is built for it, with a Lycra ribbed collar and shoulder-to-shoulder tape. The OG's flatlock seams and pre-shrunk fabric also hold up well.

Pro Club Heavyweight Long Sleeve Tee vs OG Long Sleeve T-Shirt

Buy the Pro Club if you want a thick, warm, shape-holding long sleeve that comes in sizes up to 7XL and tall. Buy the OG if you want a softer, boxier shirt with a chest pocket and a logo look. The Pro Club is the heavier, tougher build and its 544 ratings back it; the OG scores higher on its smaller rating count and owners describe it as very soft.

Choose the Pro Club if you want a heavyweight cotton tee that keeps its shape and comes in extended and tall sizes.
Choose the OG if you want a softer, boxier long sleeve with a chest pocket and a logo on the chest and back.

Prices

Pro Club Heavyweight Long Sleeve Tee: $10.99 at TFashion Mart (checked today)
OG Long Sleeve T-Shirt: $18.99 at Amazon (checked today)
Difference: the Pro Club Heavyweight Long Sleeve Tee is $8.00 cheaper than the OG Long Sleeve T-Shirt today