Tony...
I'm in the planning stages for a new bench myself, and so have been doing a lot of research on this. I've read some books, searched the internet and am now studying (that's more than reading) Christopher Schwartz's book "Workbenches". I highly recommend this book if you've actually begun the process of designing your bench. Lots of thought-provoking stuff. It's much more than what wood to use for the top, but he has an excellent discussion on that as well. Not trying to steal his thunder, but he talks about the following important properties of wood for the top:
stiffness, so it can span distance without requiring a complex undercarriage;
weight...should be heavy;
resistance to denting, for the obvious reasons.
There are charts in his book for various woods that specify how they stack up in the above areas. Basically there is not one wood that stands above all others. One of his favorite benches he made from southern yellow pine (he does not recommend white pine...too soft...although Tod would no doubt disagree). I'm using maple because I was given three logs a couple of years ago that I milled, and they are now ready to be a bench top. If that hadn't happened I'd be using ash, because I have a good supply of that, but maple is finer-grained. I have one large beech tree in my little woods but do not have the heart to take it down or I'd be considering that. Whatever you have, or can get the most economically, that meets the above requirements should do the job.
If you face-glue the boards (requires more stock but is the best way to get it 3" thick or more) then the movement of beech won't be a disqualifying factor.
Will be interested in hearing what you select and why.
Cheers.