M_Boats: Sail flat or on the side

I took my M-15 out for its first sail with me at the tiller yesterday. Beautiful day and under 10kts of wind….good for a first sail of this boat. But a question came up quickly when I was cruising across the lake. Do these M-15’s sail better on the bottom or on the side. I think that says it. I did both yesterday and using my weight could balance the boat or if I shifted to the other side could sail the boat on its side. Any opinions on that one. I am not trying to squeeze every tiny bit of speed out of her, but just wondered how others sail the M-15. I would appreciate any thoughts or experience along this line.