If you have the time I recommend working on distance first. Running farther is great for fat loss & cardio training and speed only really matters if you're trying to be competitive in races or have to squeeze your run into a confined time slot.

I also find that adding distance makes it easier to improve time. If I can only run 1 mile, it's pretty hard to run that same mile but faster. BUT if I can run 3 miles, it's a bit easier to run 1/3 of my normal distance but focusing on pushing the pace.