Boots | Always buy a size up from your street shoe to make room for stocking foot of waders.  Tight fitting boots will squeeze the blood from your feet helping to make them cold.

Felt | Better grip on slippery rocks - not great on snow/thick mud/long hikes - illegal in Alaska/Missouri/Nebraska/Maryland/S. Dakota/Rhode Island/Yellowstone National Park

Rubber | Great in saltwater - better on long hikes/thick mud/snow - bad without studs/bars on slippery rocks - greatly enhanced on slippery rocks with studs/bars

Bars/Studs | Great in fresh and saltwater - not great in rubber boats - careful stepping on lines when on rocks, bars can cut or sever line