JBJ's have a good reputation. I prefer Teco simply because if something does go wrong, they are local and the turn around is fast. Should be fine with a JBJ however. The HP on a chiller is kind of secondary to the amount you need to chill, meaning the temp drop. That is the important number. If you are not having a major heat problem requiring you to drop 5-10 degrees at a time, then you should be fine with that model. If you only need it to turn on a few times a day and knock it down a degree or three, you'll be just fine.
Example.. my Teco I had on my 140 (250G total) was a 1/3 HP... When I got my 300g I did not want to drop an extra grand or so on a 1 HP Teco or Oceanic so hooked up the 1/3HP to see how it did. Once I managed to control the flow properly, its running a bit more than it did before, but it has no problem keeping up. I say it runs maybe 1 hr a day total, in the late afternoon for 5-10 minutes at a time and I have nearly 450G total water volume on the system now. Tecos are actually more efficient and under estimated on their models for sizing.
With a 300, plus sump you'll be looking at at least 400G and most sizing charts will have you in the 3/4 HP to 1 HP.
When you get your tank and plan out the setup, just make sure your lights are off the water, you have ample evaporation and ventilation and see what happens. Worse thing that can happen is you have to upgrade at some point. So long as your house is kept at a decent temp, say below 75 and you have the right setup with good pumps and all, you shouldn't need to drop the temp more than a few degrees at a time. Its worth it to get a quality used one and see how it does next summer vs dropping 1000-1500 on a new one and find out you don't need one that big.
This is one of the few instances where I recommend buying small and trying it out first, especially if you can get a good price on a used one. Chillers hold their value so you should be able to get what you paid for it if you need to buy a new one next year.
Just make sure when you plumb and position it in the setup, you allow yourself ample room and ease of disconnect to swamp it out later if its needed.
The other thing to consider... if your AC goes out yet you still have power. While a smaller one will be fine if the house temp stays good, if you find yourself without AC in July or August but have power in the house, a smaller one WILL have more difficulty keeping up and if you are concerned with that at all, than I would make the investment and go with a 3/4 or 1HP.
