I think it's safe to say that a lot of whittling has been done over the years with Opinels. My first real projecta simple penguinwas mostly carved with an Opinel No. 6.
As you can see from yablanowitz and Trout Hound's replies, the choice of whittling knife ends up being a personal preference thing based on both what fits comfortably in your hands and what works well for the type(s) of whittling you like to do. I also like small blades, but my preference for most of my whittling is either a pen blade or a small clip. That being said, I do like having a coping or sheepsfoot handy for the occasions when I want a straight edge and a pointy tip.
Another inexpensive knife to consider is the Victorinox Recruit. If you go that route, I'd recommend removing the key ring and then either filing or grinding away its attachment point so it's not in the way of your thumb when you're working with the small blade. If you decide later that you'd like to have a straight edge, it's not too hard to modify the small pen blade into a coping blade shape. I believe that's the recommended set up of Chris Lubkeman who has written many whittling books, including the Swiss Army Knife Whittling Book.
I think an Opinel, a Recruit, or a used stockman would all be good options to get started. Get them nice and sharp, get to know them, and figure out what you like. From there, you can figure out your next move, if necessary.
Have fun and be safe.
Neat! That's some serious material removal to get from before to after.
Glad you were able to spend a nice afternoon whittlin' on your porch. Thanks for sharing what you were up to. :thumbup: