[Myka]

In reference to internal vs external, my choice depends on how much heat I want to add to the tank. Generally, internal pumps add more heat to the tank than external pumps - though this is not always the case. If your system will run cool (LED lights, in a basement, etc) then a pump adding heat to the system may be a GOOD option as it will help save on heating costs.

Are you doing a single return or dual returns? Your options will be different if you're needing one larger pump or two smaller ones. Assuming your 100 gallon sump will have about 50 gallons of water in it, you're looking for about 2100-2600 gph total return flow. If you're doing a Herbie overflow then I would suggest you use a single return pump as the Herbie will run better/easier. In that case, Sequence pumps have been a long time reliable go-to. Maybe you want a DC pump? What is your budget? What do you want out of the pump? (hot, cool, energy efficient, value, best of the best, etc)