Which haplogroup represents that collective Scytho-Sarmatian ancestry from which Montenegrins, Serbs and Albanians supposedly come from?
Not only 1 Haplogroup.J2,R1A R1B-ht35 etc
For you information,at Albanian Highlanders,R1A can be even at 15%.
As a supposition,R1A is supposed to have been more present in Scythian people,while J2,more present in Sarmatian people.
As for the Dacian connection to Albanians or Romanians,that is not true in case of Albanians.
Dacians = a thracian tribe,called Wolf-People.
Serbians have strong folk customs,linked to wolf while in Romania,in Western part,there are also some folk traditions linked to wolf.
So here is the people with most Dacian ancestry,Serbians.Dacians were only rulling class in Romania,but after the defeat from Roman Empire,when Roman Empire moved over Danube,the troops,most Dacians went with Roman Empire troops,fearing other barbarian invasions.
After in Romania came the Gothic tribes,but again,the name of these tribes was given by the leaders of the tribes,the mass of the population I do not think it was of Germanic origins,but what they have picked on the road,including lots of people from today land of Ukraine and Russia.
Anyway,the proof that both Albanians and Slavic people are descending as language mostly from Scytho-Sarmatians it is not gave by paternal lines,but from common words.
A simple cognate,between Slavic and Iranian:
Zeme - Iranian god of Earth,zemljia (aproximative writting) - earth,in most Slavic language.
zæn, zen, jhæn (woman/wife) = Bosn.
zena; Rus.
zhena (wife) in Romanian,we have zana,meaning a female deity.
As for Albanian - Iranian link,take a look at Albanian folklore and North Iran folklore and look the people.
Words?
Che - What in Iranian,Ke - what in Albanian
ku?
(where?) = ku? (
where?). - in both Albanian and Iranian language.
striking cognate: iranian kiss booseh - albanian lips - buze - romanian lips - buze
And so on.
But most strong the link between Albanians and Iranians is as I said above,the folklore,the traditional instruments,found in both North Iran and Albania.
And North Iran is also a mountainous area.