Your real determination will be, how accurately can you measure the teaching effectiveness of either teacher?
Lineage is nice, but it only goes so far in the scheme of transmission of martial skill.
You have experience with your current teacher. You can make a judgement there about his willingness to teach you, his willingness to work out and correct you and how motivated YOU are to take his teaching and develop your own skill.
Observe a class with the new teacher, don't rely on the words of others.
Get a feel of if you will click with this teacher and what his approach is.
Will you get the same level of attention that you get from your current teacher?
What are your goals in learning Wing Chun? What do you expect to gain from it?
How will you measure success?
Then, evaluate which teacher will help you reach your goals.
David Williams
http://www.wingchun.com
Kim sut, Lok ma, Ting yu, Dung tao, Mai jiang