Should I apply for MS or PhD when I am sure I want a PhD

I will finish my undergrad this summer and I am 100% determined to go for a PhD. Should I apply for MS or PhD program in CS? I have following two paths to choose: 1) Work in a research lab until 2016. Meanwhile, apply for PhD for 2016 intakes. 2) Start MS degree right after the summer and apply for PhD after MS.