I am wondering who to ask to supervise my dissertation (I'm in final year undergraduate mathematics). My interest is functional analysis and there two members of staff involved in this area. X is a professor and he is well respected, Y has been a lecturer here for about four years and is well respected here, but I'm not sure how well known he is outside of here (by "here" i mean our university). I know that I can work with y, as I've done a small project with him and he was incredibly helpful. I'm not sure if X would be willing to devote quite so much time as Y to supervising me, though I'm sure he would give plenty. My basic problem is that I know that a reference from X would look a lot better, but that I also know that I'd probably work a little better with Y. Any thoughts?