This is a highly subjective topic: what is "professional" to me may
look like junk to someone else. In my opinion, simplicity is best: not
too many fonts, not too many sizes, not too many colors, not too many
borders. In short, as little "overhead" as possible: just the facts.
Most important, probably, is to know your audience. I have made
presentations to some people for whom "no nonsense" is a religion: they
want to see data presented on one sheet, laid out in a very intuitive
fashion so they can start at the beginning, move to the middle, and
reach the end knowing all there is to know about a particular topic.
If your audience wants colors, fonts, borders, etc etc etc, then give
them what they want; if they need information only give them that; if
it's something in the middle give them that.
Cheers!
