The SNP is the obvious choice for Scottish voters for the following reasons:-
1 - They are a left leaning party, and the Scots voters are left leaning.
2 - They only care about Scotland, so everything they do will be aimed at improving the lot of the people in Scotland.
3 - They could be well be in a position of holding the majority party to ransom after the election, so they will be able to deliver real results on point 2, effectively getting the rest of the UK to fund their socialist aspirations even more so than is the case at present.
4 - They can't make Scotland independent, they can only arrange for another referendum in a few years, at which point all the lapsed Labour voters can vote 'no' again, and carry on with the current state of affairs rather than being faced with the prospect of having to pay for it all themselves.