I just completed the MSF Basic Rider Course, great course, in my opinion that is the only way to get a license. They recommended the Honda Night Hawk? 500 or 750.
I have a Aprilia RSV 1000 R FACTORY and I love it. Very responsive, light, and tons of fun to drive. You can usually find them for around the 13-15k range.
I wouldn't recommend a 250 for a beginner, imo it has too little power which could do more harm than good, especially if you need to accelerate to avoid a situation. The flipside is that I wouldnt do what I did and get a 900/litre bike as a first bike (My first bike was a 900 CBR). I would go for a 500-750cc bike just so you know if you needed it you have enough umph to get yourself out of a situation.