I feel the oil pan is the best place to install it. This is the true oil temp. Hotter spots in the system are possible but for the true temp, this is the best IMO.
I don't like the inline sender units. I really don't think they are accurate at all. I would install the sending unit in the plug next to the engine oil drain myself. The adapter is 3/8" MNPT-1/8" FNPT. Don't use any thread sealant on the threads, they are pipe thread and are tapered, besides you could loose the ground if you use a sealant.
The pan is where I want to see the temps and not in a line near the cooler.