What is the best biscuit? A question to which the proper response is “For what purpose?” Should someone respond thus, you can settle in for a good half-hour of interesting biscuity chat.
For dunking, there is much to be said for the classic digestive or the smooth purity of the rich tea. Many would speak for the robust charms of the gingernut. One would never, of course, dunk a chocolate biscuit, although these probably top the list for classic non-dunking snackage, the dark chocolate variety generally considered the more sophisticated option. Personally I find much to enjoy in the exotic foreign delights of the cinnamon biscuit, either a Jules Destrooper Almond Thin or Speculoos (not what you’re thinking but those tiny rectangular cinnamon biscuits with a pattern stamped on them that you get with coffee in continental cafes.) And it may be unpatriotic but I don’t think you can find a better chocolate biscuit than the ChocoLeibnitz, Emperor of Biscuits. The bourbon, the pink wafer, the custard cream and the garibaldi all have their adherents. For the savoury option, personally I would pick a Tuc biscuit, one of which will brighten any day, although, again, there are many who argue for the Ritz cracker, the water biscuit, the oatcake and even the Ryvita.
The jaffa cake is not a biscuit; the Inland Revenue has the right of it there. The fig roll is, somewhat counter-intuitively, definitely a biscuit. The brandysnap can generate some discussion, but is usually considered by experts to be a dessert rather than a biscuit, purely on the grounds that a biscuit is not normally improved by the addition of whipped cream (although one might mention the infamous Gingernut Log, in which an entire packet of gingernuts is sandwiched together and then covered with whipped cream and refrigerated to produce a dessert as rich as it is delicious).
Please don’t mention cookies, those vulgarly sized, under-baked transatlantic vehicles for lumps of unpleasant cheap chocolate. They are not biscuits, and never will be.