Fraser on Straddie are both great places to visit. Both have there advantages
If you are worried about distances the I would opt for straddie there are still some paved roads more people if you get in to trouble and the ferry is cheaper. There is also a bretty good pud that goes off on a Sunday afternoon.
But in my oppinion Fraser is by far better for a couple of blokes a lot of beer and fising rods, it is more remote and there are less families. It does have disadvantages like not being able to swim in the surf but there are still the champagne pools and the lakes to visit. And did I mention the fishing and off roading is better.
About Byron been there a couple of times but never really looked in to driving on the beach as I'm not sure that you can, I might be wrong though. It's also a great place to visit, but as wierd as it may sound ever time I go there I have found it to be a very comercial based alternative life style type of sceen if you know what I mean. This may just be me though or also the times that I visit. They also have a great pub on the beach that is worth a visit and the food there is just amazing burgers that fill the plate that leave little room for the salad and chips.
Adam