2-part dosing vs calcium reactor
 

What do you guys think would be better for a (100gal water volume) reef tank, 2-part dosing or calcium reactor? what is easier than the other in the long run?

That will depend on your needs based on the livestock you choose. If you are housing mostly soft corals and some LPS corals, a standard 2-part should suffice. If you are housing SPS corals, Your system will have a higher demand, and will benefit from a calcium reactor.