It's really going to depend on the size of your hand and how you prefer to grip (or not) the mouse.
I've used the deathadder - I would give this a recommendation as being a very comfortable mouse to use. Not sure how to explain hand sizes, but I'd say I have 'medium' or 'normal' size hands. The mouse was large enough that I didn't have to really grip the mouse, rather just lay my hand on the top. My friend who I would say has 'big' hands also used a deathadder and agreed that it was comfortable, but is currently using a Steelseries Sensei a reckons it's comfier than the deathadder due to its slightly larger size.
Currently I'm using the Logitech G402 - it has a few extra buttons compared to the deathadder, but is slightly smaller and therefore requires I grip the mouse slightly. Not a huge issue, and I haven't found it is uncomfortable when playing for 5+ hours. The extra buttons have proved exceptionally useful for me.