If your surgeon lists both then you can choose which one is easiest, it can't be wrong for you if he is recommending it. Don't worry about the sugar, it is a total meal replacement shake, you have to get energy somewhere. Also if you're sticking to pre op then a couple of grams of sugar in your shake is not going to cause an issue.
I've used both, but I had to do opti with my surgeon.
I love chocolate in both! I would buy the other flavours when I was doing TF but always ended up sticking with drinking the chocolate. Plus tony ferguson had a chocolate cherry and a choc macadamia.
I did eat a few of the opti bars pre op, when I was out and about I found them really handy. I don't use them now as I find them too big. Now I keep some 30g low carb protein bars, protein fx or musashi for emergency snacks.
I agree with Katey, the colder the better. When I did pre op I bought myself a Nutri Ninja Slim blender from big w in preparation for post op purée. It makes the best protein shakes!! Chuck in some ice, a sachet of Shake and a small amount of water ...voila awesome icy shake with no powdery lumpy bits. Tastes way better that way. Now that I'm post op I put half a shake, liquid multi, ice and water to make up to about 200ml, as I can't fit any more than that in at a time.