I've been carrying mine in a Stealthgear IWB holster for years. The original one was nice, but the "mini" is extremely comfortable. They're tuckable and easily removable with J clips. I've been very happy with their products.

I had an original size Ventcore for my Shield that I sold and moved to the Revolution "Mini" when it came out. I wanted to try the smaller size but didn't sell the Ventcore until I tried the Revolution for a bit.

I carry a 19 sized gun in a Ventcore Mini.

I'd say the Ventcore is a little more comfortable with the padding, but the Revolution is perfectly comfortable. It's a personal preference thing that I don't think you can go too wrong with. I like having the padding on the larger framed gun. I think the Revolution is a little lighter as well, so it pairs well with the Shield.  

I think the bigger difference is moving to a smaller footprint holster with the Mini. I like the Mini size a lot more than the standard.