Personal preference perhaps, but I like using fresh to infuse. It's how I make water to drink in the summer, so I figure I might as well use the same process for other infusions. The compounds/oils in the herbs seems to diffuse more readily into the water with fresh.
I think a lot of it has to do with availability and cost and common sense. I have a plethora of lemon balm, sage and thyme in my garden, so could feasibly use fresh, but I can't grow rosemary to save my life or know anyone that can. I'm not going to pay $2-$4 for a little bundle from the grocer, so it's easier to obtain dry. Oh, and you usually need more raw material than dry.
There is also the matter of season and spoilage. Where I am, we have at least 4-6 months of snow, so fresh during that time isn't even an option. Doing a bulk infusion with water to last for winter would either take up valuable freezer space or run the risk of bacteria growth, so dry, make it as you need it is the best option.
Long story short, either works, just do what works best for you.
I think a lot of it has to do with availability and cost and common sense. I have a plethora of lemon balm, sage and thyme in my garden, so could feasibly use fresh, but I can't grow rosemary to save my life or know anyone that can.
I had to laugh when I read that. When I lived in CT I could grow the same things as you - but my rosemary died. Now here in Arizona I'm struggling to keep my basil and oregano alive but the rosemary is taking over! I'm not doing anything to it either, its on a drip line once a day. I guess it likes temperatures over 100 with very little water!
I can not complain, rosemary is growing like crazy, I just put the first dry portion in the jar, and cut down a lot for drying (I love it in my meat stew) Basil is so so, due cool nights this year. Oregano is taking over my herb bed so I am kind of drying then fighting with it) Dry herbs are not only safer in infusions but as was said is much more practical with the storage