Square coolers IMO are superior, I have had mine for almost 3 years, it is just now beginning to leak around the ball valve, but I think I can fix it with some PVC, and Great Stuff.
Plus you are really limited with a round cooler unless you don't want to do 10 gallon batches of mid-gravity ales your okay.
In addition, I use a 3/4" water heater supply braid, and have had absolutely no issues with lautering.
Even with 24lbs of grain on it, no problems, I have only had one stuck sparge due to a considerable amount of wheat in the tun, but otherwise really no issues, costed about $12.
FWIW, I use a 52 qt Coleman Xtreme, and I usually brew 10 gallon batches. 5g batches works well with the 52qt size, but take a little longer for mash temps to equalize, and loses about 1 degree over an hour opposed to when I mash for 10g, unreadable temp loss over the 60 minute mash with my Thermapen.