They are completely different coins in different fields. QTUM is a platform coin combining the best of Bitcoin with Ethereum. They provide a backend that other coins can ride on.
OMG is a financial ecosytem that provides payments and banking. They both have huge potential but in my opinion QTUM’s growth is halted until China changes their stance on ICOs and Bitcoin in general.
Few days back qtum was $8 and today it's shooting and already reached $70.