Round thumbhole vs. oval thumbhole, Im planning on switching to oval thumbhole, just wanted to know if anybody has tried this, is it better? or is there any diffrence? Just want to know some of your opinions or comments. thanks!

It all depends on the shape of your thumb.
If it's more oval than round shaped  when you look at it from the tip its probably a smart move.
Also how much do they open up your thumb hole after drilling?
How much tape do you need to make it fit comfortably.

Personally I use an oval thumb sleeve just turned to match the flat spot on the back of my thumb. No bevel at all.
It works for me but alot of people might hang up in this combination.

I use urethane thumb slugs drilled out to an oval. I like the feel of this because my thumb swells and shrinks alot. So i put 3 or 4 pieces of tape in it and even when my thumb swells i can still get a clean release. I use white 3/4"
tape at the front of my thumb hole and i build it so its a little tighter around the knuckle.

Almost everybody’s thumb is oval so why not their thumb hole?

You can still shape the oval inserts some. Start with one that is relatively tight and then sand out the tight spots to shape it to your thumb.