Need help picking a cooler mash tun

[gotbags-10]

So I am going all grain and need a cooler mash tun. I will mainly be doing 5 gal batches but would like the possibility of doing a 10g batch. I normally do IPAs. I'm assuming I need at least a 10g cooler but I didn't know if I should go wit the round igloo/ Rubbermaid or a rectangular? If I go with rectangular any recommendations on which holds temps the best. Thanks nick

 

[Blitzkrieg]

I've never tried the round coolers but my mash tun is a Coleman extreme 48qt. With 12 lbs of grain it loses 0.9 degrees F in 60 mins. It was however a pain right in the butt to get a seal on the bulkhead. They drilled the hole for the drain at the very bottom so the gasket doesn't sit on a flat surface. Beyond that I'm happy with it.