PayPal (NASDAQ: PYPL) and Square (NYSE: SQ) are two of the biggest names in financial technology. Both companies provide the same value to merchants; they help them make more sales. PayPal excels in the e-commerce space while Square has built up a network of brick-and-mortar merchants. But both are increasingly moving into each other's territory.Both stocks have performed well in 2018, but Square's 78% price increase year to date dwarf's PayPal's 13% jump in share price.