Ideally stick to one or two instructors unless you are having a problem with that instructor in which case you might need to change. Flying with more very much depends on how good the club standardisation is, I did my instructors ticket at a club where all the instructors had been trained in house, so all taught pretty much the same thing, though differing instructors might teach in a slightly different way, other clubs can have all the instructors teaching a different method so little standardisation - not so good.