I had the Xoom, returned it for the Transformer, then returned the Transformer for the Galaxy tab 10.1. I will be keeping the 10.1 and love it.
The Xoom screen is TERRIBLE and it's way too heavy. And up until recently the Xoom was the most expensive tablet on the market, despite having the worst features.
The Transformer was just a big POS. Software was extremely slow on laggy, build quality was abysmal.
I have no need for microSD or HDMI so that was no big deal for me. what I wanted was a light tablet with a wonderful screen and high build quality. The Galaxy tab 10.1 is the only one that gives me that.
What the Xoom has going for it is that it is the first to get Honeycomb updates, and it's built like a tank (in a good way, meaning it's sturdy).
I would use the $100 Staples coupon and get the Galaxy Tab 10.1. Thankfully it is still shipping without Touchwiz, since I don't like how Touchwiz tries to make Honeycomb look like iOS (seriously Samsung, get off of Apple's nuts already, it's embarrassing).