I think it really depends. Obviously respecting fans will buy their OS of choice. What is left are the people in the middle. If the fact that the Transformer can almost fully replace a netbook/laptop is pushed, then I think it will win. If not, people will go with the brand they know, which is the iPad.
That being said, the iPad, just from a hardware perspective is sexier being more compact and lighter, without a huge bezel. However, the Transformer has all of the benefits of Honeycomb's openness, file system, etc. I think it will come down to whatever people value more. Form vs function.
Also, correct me if I am wrong, but the transformer at $399 doesn't come with the keyboard dock, which I have heard will cost $150 extra.