Velux hot water system

Jerry, I would recommend flat plates. If you ever add to the system, it's a lot easy to match and connect flat plates. Evacuated tube designs are still changing to rapidly.
 Is the front of the house and the roof the only location you have to install the panels? Where is the hot tub and other utilities located? How much piping will be needed? Is snow a problem where you are located? Is there room for expansion? Can you add a second, cheaper hot water system dedicated to the tub? How many panels are you planning on using for both the tub and domestic hot water?.....
 Just some other questions for you to think about when installing a SHW system.