I'm in the group of "If you cannot say something nice.....".
My Mother taught me this and she lived what she taught until she was well into her 80's and then she became more outspoken.
I had a woman look at one of my needlepoint projects. It was a fun sign to hang outside our RV. I did not follow all the rules or pattern so the back was messy. She said "How cute" and then looked at the back, and said "Oh, my!" I thought she was rude to look at the back!
It is best to say something positive about a quilt if you are in person. I agree you can admire the colors or pattern or simply say I know that took a lot of work.