one of thing which I find interesting about the Mendelssohn Violin Concerto is that it is a rare work that seems to be played slower and slower with the passing years. Take for example three of Francescatti recordings I have heard, between the first with Szell and the last (and my favourite) with Dorati there is a full three minutes difference.
Personally what I look for in this Concerto is a soloist that wears their hearth on their sleeve, and that has a beatiful, sweet singing tone throughout. Vengerov achieves that wonderfully in his Teldec recording with Masur/Leipzig. Pity that the orchestra does not quite sound as beautiful as he does. Other recordings I like are Kogan with the USSR State Simphony, Oistrach/Leipzig and the Francescatti/Dorati I mentioned above.