Which example is better?
There are three reasons for this: One, two, finally.
There are three reasons for this. One, two, finally.
Which example is better?
There are three reasons for this: One, two, finally.
There are three reasons for this. One, two, finally.
Welcome to the community.
You would be well advised to go with option No:1 - The colon.
A colon is used to explain or start an enumeration.
i.e. I have three sisters: Daphne, Rose, and Suzanne.
If you want to dig deeper into the matter, use one of the numerous online resources.
Here's one to get you started and hopefully shed some more light on any doubts and uncertainties you might have regarding the use of colons and semicolons: https://www.boundless.com/writing/textbooks/boundless-writing-textbook/style-structure-grammar-5/punctuation-31/using-semicolons-and-colons-141-10151/
You might also want to keep an eye out for closely related topics such as Colons and semi-colons in order to avoid asking questions which already have an answer here on EL&U.