Unicycles

I'm thinking about getting a unicycle.

1. What size would be good for eventually trail riding. I'm 5'5" if that matters much.

2. Brand choices? I've been looking here in the <$100 range.

3. There's 1 with training wheels Rand Ross 20" Barracuda Unicycle with Training Wheels. Thoughts?

4. Anybody have one they want to give up?