reasons I use shards: higher dps (duh lol)
reasons I use shell: With shell I can run face-first into magdas bugs / stand on arcane axis for several seconds, making magda/sk fight incredibly easy where as shards will require me to be a bit more attentive during that fight haha.
I generally only run ubers in mp10 and usually I'm carrying people so it's important that I don't die even once (making shell the clear choice). But since I am usually carrying people that means there is usually a lack of dps and increasing my dps is useful for quicker fights (making shards the better choice).
I tend to switch back and forth depending on how lazy I'm feeling / how important it is that I dont die ever - I'm just curious what others have found they prefer for ubers?