Hello and welcome to the forum Lush
When you ask which lasts longer, do you mean overall life or per refill? The answer is different for each.
The cartomizer will hold roughly twice as much
juice as the cartridge for a 510. So fillups would be much less often with the cartomizer. Overall life span, the cartridges if well maintained last a long long time.
I much prefer the simplicity of cartomizers myself.....but try both, others will be along to disagree with me

When you are first starting out, all the choices can seem daunting. It gets easier over time and the good thing about all the choices is that it is highly likely you will find something that works for you.
Good Luck and
vape ON!