When comparing Kerbal Engineer Redux vs Hot Rockets, the Slant community recommends Kerbal Engineer Redux for most people. In the question“What are the best Kerbal Space Program mods?” Kerbal Engineer Redux is ranked 1st while Hot Rockets is ranked 5th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Helps with designing functional and efficient ships
Pro Shows important statistics when building crafts and in-flight
Shows important statistics when building crafts (mass, deltaV, thrust, ISP - while on Kerbin, in vacuum, or on other atmospheric bodies) and in-flight (all of the above + periapsis, apoapsis, orbital period, time to ap, time to pe and many many more).
Pro Provides customizable in-flight readouts of flight data
Pro This is not an autopilot
As opposed to MechJeb, which is considered "cheats". KER helps a ton by providing already available info in a very accessible manner.
Pro Very low memory cost
Pro Improves engine effects
Cons
Con Less readable than some alternatives
The same information is presented in a more intuitive and readable way by DMagic's "Basic Delta V" and "Basic Orbit".
Con The fuel readout shows about 50x more fuel then you actually have
Con Unsupported by most mods
This is a very old mod, and as such the modding community has moved on to configurations for different systems. I don't even think the mod is up to date with the most recent stock parts.
Con Better alternatives as of 2021
RealPlume and Waterfall have better performance, look better, and supported by most other mods.