The NightForce 30mm Steel Ring Set that I would recommend for your Springfield Armory Saint and riflescope are the Extra High rings. The Extra High rings will provide a 1.5" centerline height which is the ideal centerline height for an AR platform rifle, regardless of the size of the objective lens.
The A101 30mm medium ring should do just fine in this application.
To mount the NF NXS 5.5-22×56mm scope to that rifle I recommend using the 1.125" high model or 1.376" extra high model of the NightForce 30mm Steel Ring Sets. However, currently the only model available is the Extra High Model.
The rail you would be looking for is either the A328 for 0 MOA and A296 for 20 MOA. While the 20 MOA base may not be necessary in your application, the scope has enough internal travel that even with it you will have no trouble achieving a 100 yard zero. You may never use the extreme ends of the travel but adding the 20 MOA will likely keep you in the scope's "Sweet spot" for longer in the up elevation adjustment range. The rings I would suggest would be the A107 Xtreme Duty Ultralite High ring set. This should provide clearance for flip caps.
Nightforce rings are designed and machined to work with Picatinny spec bases and will not torque properly to a Weaver Spec base. For height, anything from the .885" low ring on up will clear the objective.
Medium rings would be best. Low might work too but the eyepieces could interfere with the bolt handle.
Please contact us at techsales@opticsplanet.com with the make, model, and caliber of the rifle you are mounting it on.
You would want high rings for that setup.
You should be able to safely use medium height rings on that setup. MPN: A100
The Nightforce 34mm ring set can be found here : https://www.opticsplanet.com/nightforce-ring-set-34mm-ultralite.html