Not sure what the rest of you are saying but here's my take,
Internal has its pros and cons but being more detectable is not one of them... with internals the esp, aimbot ect are usually smoother and faster as it is internally getting the data where as external has to read the memory before it can then write it (causing a delay).
Externals are usually preferred by cheat developers as they are easier and also you don't have the issues of violations within the game files, this is more predominant in games with AC such as PUBG/Fortnite and such.
For your case talking about CS:GO Internal v External they are both as detectable as each other however making an UD external is easier. Once both are made they are just as likely to stay UD/get banned as each other unless there are numerous people using the hack. If more then 20 or so people are using an internal detection rate increases due to many factors.
My advise to you is if you are making this cheat (not likely due to the question you have asked) then go with external.. if you are another paster then don't bother with either and if you are a gun at coding go for internal as it will always produce the better cheat.
P.s you can do everything in a external that you can do in a internal, including skin changer