I dont know where you are in NH but there is a solar co-op in the Plymouth area that does bulk buys of Apricus evacuated tube collectors and has weekend installs. Their website is
http://www.plymouthenergy.org/. They have several installs coming up and each install, has an open house.
I have flat plate collectors with a DC pumping system run by a 40 watt solar panel. It is very good at generating lots of warm water but not so good in the winter at generating hot enough water. The evacuated tube collectors are less efficient but are better at making hot water year round. Bascially a flat plate system will generate water no more than 80 F warmer than outdoor temp, versus evacuated tube can go 200F over the outside temp. So if you want smaller volumes of hot water year round directly off a solar panel go evacuated tube, if you use larger amounts of hot water and have a efficient means of stepping up the temp, go flat plate.
Some trade offs for evacuated tubes are
More fragile, (consider that the tubes are basically thick fluorescent tubes laying out flat on your roof).
You need to find a way to dump the heat in summer as the fluid will boil and pressurize. Alternately you need to come up with a way of covering the panels when you dont need the heat.
You want to make sure your pumping system is robust as overheated stagnant fluid in the tube header will breakdown quickly.
As for DC pumping with a PV panel, it sounds neat and runs during a power outage, but it adds $400 to the system cost (note, most of the kits that are sold with DC pumping use a 20 watt panel which is insufficent to run a system in NH). I would install a 110 AC Taco cartridge circulator with a differential controller. The DC systems usually sell themselves as no need for controls "when the sun is out the pump runs", that is not fully true, it will work but you will lost some heat in the mornings and evenings when the tank temp is higher than the collector temp, yet the pump runs. There is a DC controller built by a guy in Maine (artec?) that works well to get around this issue.
And lastly, make sure that you have mutiple check valves in the system and inspect their operation on a annual basis. Most of the failed systems from years past were taken out of service due to reverse thermosyphoning on a real cold night. If the check valve fails open, the system will send all the heat to the collectors on the roof and freeze the potable water side of the heat exchanger (usually bursting it).
Drop me a PM if you have more questions