First of all, the sides from deca are not as common as some would have you believe. What I would do, since this is your first cycle is go with whichever one is cheaper, and plan on doing the other next time out. In this case, you could get the deca cheaper, so I would go with that. Can you get sides on 300mg/week of deca? Sure. But you have about the same chance as getting sides on 600mg/week of eq. In other words, very little.
Also, I feel eq at 400mg/week is not that effective. Some get good results from it, but I haven't seen many. I think it acts more as a tonic at that dose. You know, increased appetite, some cosmetic changes, but not much else. If you need to bulk up, eq at a low dose is not going to do it.
But, whichever one you ultimately choose will be fine. This being your first cycle, and test/deca or test/eq both being excellent choices, get ready for some real growth.