I wanted to share some facts about these two languages for many reasons. Feel free to contribute your knowledge or chat about either of these languages.
Many people confuse the two or sometimes just assume that there is one "Scottish", the tongue of Scotland. There is, in fact, more than one language native to Scotland, each with different names. Scotland's official language is English, but British Sign Language, Scots and Scottish Gaelic are all recognized minority languages.
Here are the differences (big ones!)
Scots is a lot like a differently spoken/written form of English. An English speaker can easily understand a lecture or text in Scots, as it is a sister Germanic language of English, but there are many differences such as spelling and pronunciation, making it strange and even laughable to those who had no idea it existed. There are about a million and a half speakers of Scots, mainly but not exclusively in Scotland.
Scottish Gaelic, on the other hand, is a Goildelic Cletic language more related to modern Irish. In fact, I think if one can speak Irish with fluency, Scottish Gaelic is likely to be as easy or easier for them, since both are descended from Middle and Old Irish. Knowledge in Scottish Gaelic is rarer than knowledge in Scots, as efforts to revive Scottish Gaelic has been laughed at and looked down upon by the general population of Scotland (at least in past years), but less than 90,000 people have any knowledge in Scottish Gaelic.
Here are examples to compare the two further:
University Lecture in Scots: https://www.youtube.com/watch?v=cENbkHS3mnY
Man speaking in Scottish Gaelic: https://www.youtube.com/watch?v=hwQbxuwXGhc
Wikipedia article about English