when you go to places that are remote,(and you do get them) you can't just pop down to you local divers shop for a refill, so in my personall view its best to have both, yes its quicker and easier to fill with a bottle but you lot must all be very "puny" if you find it hard work pumping the gun up,after all its just a good arm workout , and makes me feel all pumped up too.
The knack (if you struggle) is to bend your legs at the last 3" of stroke and use your body weight to push down, then you will have no problems, and as for the comment pumps give you heart attacks or something along them lines, im sure if you dont do any pysical work its more likely to bring on heart problems,this could also be a good cardiovascular workout each time.
So it's got my vote GET A PUMP