For me it has to be the Flower Class corvettes.
These little beauties (i feel) are always overlooked for the sterling work they performed.
Ok so they didn't have big guns or handsome lines (and i think traced their DNA to a trawler) but I like to look at their abilities from another perspective; i.e. not from how many ships they sunk but the tonnage that wasn't!
No action, (but dogged, terrier-like perseverance) was a good day for these old girls.
Flower class corvette - Wikipedia, the free encyclopedia
Oh, and any hard-chined MTB / rescue launch with a temperamental engine and 4000+ horsepower, because when you are not fearing for your life (and kidneys) must have been quite exhilarating!