Having only ever had one instructor I can speak from great inexperience!!. .. .I got on really well with him, he's about 20 years older than me, been in aviation most of his life and we always stop for a chat when our paths cross. . .. .So IMHO, find an instructor you like (you going to spent 40 hours or so in close proximity) and stay with them. Ensure the club doesn't roster you with whichever instructor is free.