Is it easier to go from Army Reserves to Active Duty as an E-4 or E-5?

As a former recruiter who worked with a few reservists, the best answer based on my experience is, you will regardless a rank verification. In order to retain your rank, let's say E5, you must show proof that you meet all requirements an E5 in active duty needs, BLC 1059, NCOER, complete SSD, etc.

The unfortunate answer is, 'it depends'. Generally they are looking for a specific MOS, grade, and SQI. If you're a 35P airborne SPC and they want a SGT, you're hosed. Likewise if you're a SGT without the identifier.

18X is normally an option regardless of your current skills.
If you want to look at AGR, SGT will increase your chances (especially to be a 79R).

I’m a recruiter right now, the current business rules make it easier for NCO’s to transfer compared to the beginning of 2015. E4 and below have an MOS list at MEPS or if in an MOS needed may get orders directly to a unit. E5 and up do a “grade determination” which includes the MOS’s you can retrain to, where you can get stationed if no retraining, and how long you have to get whatever NCO school done if required. When I first came out to recruiting the stars and planets had to align to get an NCO with the perfect combination of job, airborne, time in service. E4 and below were easy though.