Quality Diesel stations in Boston area ?
Coming along the MA Turnpike, you will find Mobil diesel at reasonable* prices.
There is another plaza (Mobil diesel, IIRC) that people exiting the Turnpike will come upon...it's about 1/2 miles south of the 'pike on Rt 128...big place with McD's, etc.
Coming from the MA Turnpike and headind south on Rt128/I95, you can hit the following locations:
Take the Rt1 (south) exit and travel for about 1 mile. You will find ROJO which offers the lowest prices on gas and diesel in the area. I think it's Sunoco...it changed ownership recently. They sell a ton of fuel.
You can exit Rt128 at the Rt138 exit and head north and will immediately come upon a Gulf which sells the "Autodiesel" product even though the pump is labelled "Dieselect". This is about 5 miles from the hotel.
Sprague is in Quincy but would be challenging for most to find. This station is located right at the tank farm.
Braintree is a "city" and I'm certain there is plenty of diesel around. In general, you will find diesel at many stations in the area...that is not a problem.
The boutique diesel dealer, Burke Oil in Chelsea, is somewhat difficult to get to.
*based on regional averages