Which dialect / regional variant do Germans like the best?

Apparently it's Bayerisch. The online poll also puts Nieder-Plattdeutsch (Low German) in first place with Bayerisch, and personally that's also my favourite simply because it resembles English and Dutch so much and in an alternate history it would have been nice to see that as Germany's official language in order to create a more unified Germanic language continuum. Wikipedia has a nice illustration of some vocabulary in these languages, and you can see that German often stands out on its own.

Proto-Germanic	High German	Low German	Dutch	English	German	Frisian
k	ch	maken, moaken, maaken	maken	make	machen	meitsje
k	kch	Karl, Korl	Karel	Carl, Ceorl, Churl	Karl	Kirl, Tsjirl
d	t	Dag, Dach	dag	day	Tag	Dei
t	ss	eten, äten	eten	eat	essen	ite
t	z (/ts/)	teihn, tian	tien	ten	zehn	tsien
t	tz, z (/ts/)	sitten	zitten	sit	sitzen	sitte
p	f, ff	Schipp, Schepp	schip	ship, skiff	Schiff	skip
p	pf	Peper, Päpa	peper	pepper	Pfeffer	peper
β	b	Wief, Wiewer	wijf, wijven *	wife, wives	Weib, Weiber *	wyf, wyven

I would translate some of the article but really it's a subject that only those that already know a fair amount of German would be interested in.