26" or 29" cruiser Which one "New in the Game"

if using the rag joint, then 36 spokes is important

there are 9 bolts to secure a rag joint for the rear sprocket - if the number of spokes of the rear wheel isn't divisible by 9, it will be very hard to get the sprocket on straight & tight

some 29s have weird spoke counts, most 26s have 36 spokes which is about the perfect number

if both bikes you're looking at don't have 36 spokes, then pick the one that does

Why not have both. I put a 29" fork on my 26" frame and I'm very satisfied with the look, the feel and the ride.
Also before you mess around with a standard sprocket setup attached to the spokes, consider a rear sprocket adaptor. You will need to step up to a 415 chain and a 415 front drive sprocket. Some simple cutting and grinding on the cover plate for chain clearance is needed, but the 415 is much more reliable than the standard 210 chain. The adaptor and sprocket are machined from billet aluminum and are considerably lighter than the standard set up made of steel.
The adaptor puts the torque to the hub where it belongs, and you have a wide verity of sprockets to choose from.
The adaptor requires a 1.5" dia. rear hub, 36 hole rim with a 4 cross spoke pattern. It takes all of about 5 minutes to install and adjust. Don't forget to use locktite on everything... Have fun.

though I sell sprockets modified to fit coaster brakes, and will do repairs on them, I refuse to build a coaster brake setup for a customer