If you're referring to the Essential collection where one has a sleeve vs one doesn't...thoughts below. If you're referring to the Essential Cabin vs Essential Cabin S -- then I recommend the standard Essential as it's slightly bigger with more space.
Really depends on your travel style/preference. Personally, I always have a personal item in addition to my carry on (e.g., a book bag/briefcase for work) that I can store my laptop/other necessities) so I don't find a need for the sleeve on the luggage.
If you'd like the convenience of the sleeve to quickly access your laptop or whatever slim, non-bulky item you have during travel and don't want to fit in your personal item, then go for the Essential Sleeve. Otherwise, an outside sleeve on a Rimowa takes away from the "true" Rimowa look.
Cheers!
Last edited by worldtrotter9210; Jan 20, 2019 at 5:50 pm
Reason: Added more information to my answer.