The main difference is Strawpoll is for non-ranking polls, whereas deckrank is for ranking polls. Voters on a deckrank poll can rank options in order of preference, which is useful when figuring out collective choice in many situations. For example, here're the results from a poll on products announced at WWDC 2015: http://deckrank.co/v/EyxcM08gL and here's the voting page: http://deckrank.co/r/415zA8gL