I'd go for 4 years. I'm graduating in 3 years, a transfer student as well. It's not about the time, it's about what you do and learn. If you can learn all that you need for your masters program in the time that you have left, I can't imagine why you would need a reason to stay other than to waste time, money, and take a few electives.
Go for the 4 years...it looks better and is kind of expected anyway.
Good luck getting into the MAcc program!