ALWAYS go bigger. This is MFK. I have a 30 inch high tank, and that is the most height I would get for 2 reasons.
1. It's the deepest tank I can touch the bottom and clean the bottom of the glass with my arm without getting in it. I'm 6 feet tall, if you're much shorter than me, then don't get a 30 inch tall tank.
2. 32 inches is how wide the door is to get a tank into my house--I don't have a sliding glass door, all my doors are 31-32 inches wide. Any more than 30 inch height tank, I'd have to take a window out to get the tank in. No thanks.
So, you're a go for 30 inch height unless your arms are a lot shorter than mine. If they are, then get the 180.