What is your favorite position to enter against smaller but faster and more agile people?

My favorite is side control and getting into arm choke position. I'm very tall and big and have a hard time with faster opponents. I know that as a 6'8" 250 lbs woman I have special conditions but getting into good positions early while I'm not so tired is important. I've competed a few times and lost all of my matches and although it's been incredibly fun and exciting, I have major problems using my size.
Does anyone recognize themselves in this?