I have the biggest deadblow that HF? Northern Tool? could sell me ten years ago. I love it. Get the biggest one you see. You can always buy a smaller, cheaper one later. I love dead blow. Big hits, no bounce. You'll never realize how much hammers were bouncing back on you until you get one. I can't say the force is truly transmitted more efficiently (that's been settled here, some thread) but it sure feeeels like it to me.
Like a poster above, yeah, my "4 lb" hammer wasn't that heavy. But it's still big and heavy. If I wanted to go bigger, that would be from a real brand like SO & Stanley, and that's real money.