I'm in agreement with most everyone on here. If you've NEVER ridden on anything other than the lawn tractor, maybe a 50cc 2T would be appropriate for you.
If you have some riding experience though I seriously recommend a 150 or better. Of course as mentioned you'll want to check the laws in your state or county. Some areas have a "local" way of handling scooter issues, Some will and some won't enforce scooter laws but to be safe, I'd at least make it legal. Riding gear is VERY important! One good lay down of your scooter will explain that so don't cheat yourself into thinking it won't happen. Of course though I hope it never does.