Imo here is my pros and cons
Insump - Pros- Less noise, if the pump leaks it leaks into the sump, can add needed heat.
Cons - Can add heat if not wanted, Chance of stray current.
External -Pros - Not much added heat, usually provides more flow
Cons - Noisier, if pump develops leak it could cause water damage.
Im sure there are more but those are just the few I considered when deciding to run a pump.