Which would you choose: 15 or 20 gallon mash tun?

I happen to have both a 15 gallon stock pot and a 20 gallon stock pot available, one of which I am going to convert into a mash tun. The one not used is just going to sit around as a spare, since I have other pots for my HLT and BK.

I'm probably not going to do 15 gallon batches, and so I am wondering if there would be any benefit to using a 20 gallon MLT for 5 and 10 gallon batches? The one advantage I am thinking of is that it would spread the grist over a larger false bottom, possibly allowing better extraction and less chance of a stuck sparge. I am going to be recirculating. The disadvantages I can think of would be that there would be more loss to deadspace, and possibly worse temperature conservation.

Any thoughts on which would work better?

The recommendation is to have at least 8 inches of grain bed depth in the mash tun to form an effective particulate filter. So, if the 20 gallon pot has a large diameter (e.g, 18 inches) and you're only planning on doing 10 gallon batches, then I would lean towards the 15 gallon tun.

There is also the weight consideration if you move the pots around...Increased thermal loss, etc.