Tun Options... I'm Torn

I'm torn on choosing a tun.

I have a keggle BK currently. I may go with a sculpture some day, who knows. I do mostly 5 gallon extract full-boil batches right now, but am eyeing 10 gallon all-grain batches. And I'm having trouble chosing my tun, knowing that I need probably at least 50 qts to be happy. For now, I know I want to be able to do at least 10 gallons of 1.074 AG.

I own what I calculate to be about a 52-quart rectangular cooler that I could covert. Or my HBSS has some pre-made round cooler tuns I could buy. Or NB has one on sale today. Or I could buy a 100 qt and convert it. Or I could go Keg MLT.

I've read tons of threads, and I'm no closer to choosing. This is very rare for me to find it so hard to choose. Can anybody provide insight, or possibly, regret into their decision and how they feel about it now? That'd really help me choose.

Use your rectangular cooler. I do 10 gallon batches in mine with a cvpvc manifold in it. I am welding together a brew stand as we speak. Its nice to still brew while i work on my sculpture. There is a ton of threads on here to do it on the cheap and i hit over 80% efficiency on batch sparge with it.