Again, according to my experience. I strongly suggest you to DIY.
1. The immigration application is not very complex as you think, only you need to spend some time to ready and study all the necessary information on CIC website, but I don't think it wastes time because you may understand more about Canada,such as what they need and what their work style is and so on. The most important, it is the good time for you to immprove your English;
2. Another reason, DIY could shorten your application time less or more. Because you have shown your condience to VO when you submit your application to CIC after your DIY; As I mentioned before, confidence is very immportant in their eyes;
3. The last and the most important, DIY could save money for you. ^_^
Maybe my comment may raise little objection from some agent here. I can only say sorry la.
I'm also confused about this point,maybe agent is a better choice.It can help you avoid some difficulties,but the fee is comparatively high.Think it over and make the best choice lo