Remember that the size of the fiber dictates light transmission too. Because of that if I use .10 pins they are only for longer range pins. If had choice between the two personally I would go with .19 so they don't go dark as fast. You could had a light I guess but I don't like to do that.
A .010 is to small for my old eyes. I actually went to a .026 top pin now. It gathers/transmits more light and I can see it easier than the .019. Also at 20-25 yards it isn't too big that it covers your target.
If it helps your decision making, the React Pro will have a sight light on it to light up the pins in low light conditions. Won't illuminate the animal, just the sight pins. I have a used it before in blinds and in a barn and it works great. The brightness will also be adjustable and the lowest setting is more than enough light added to see them. I have the .019 and I've only had to use the light those two times I mentioned. It gathers light like crazy and often times the pins glow bright before there is enough shooting light in the morning.
I shoot a HHA 5510 Tournament Edition. I think the .019 pins cover to much of the target. I shoot way tighter groups with .010 pin.
I have the Pro with .019 pins, but I have also had a react one and a React One Pro with .010 pin and with Trophy ridge you get really bright pins either way. They also have a light on it which to me really is only helpful for a ground blind. The pins are really that bright without the light. I find that the .019 pins are fine since with the react 5 pro you are really only shooting 20-60 yards and they don't crowd each other out too much. The ideal to me would be .019 20,30,40yards and .010 50 and 60 yards. With that said I think you'd be just fine with .010 as well. I would probably get whichever one you found at the best price and be happy with either. Another option which is what I went with on my current set up is a MBG ascent sight 3-5 pin and you can customize pin size and color just how you like it. I have .019 at 20,30 yard pins and a .010 40 yard pin that also acts as my adjustable floater pin out to further distances.