If you have never bought anything in this category, the choice is the hard part. Here is the short version of what actually matters.
Material first
Body-safe silicone, ABS plastic and borosilicate glass are non-porous, which means they can be cleaned properly. Anything described as "jelly", "TPR" or simply "rubber" is porous and cannot be. Start with silicone.
Smaller than you think
Almost everybody's first choice is too large. Dimensions are on every product page for this reason; measure something familiar against them before ordering.
Lubricant is not optional
Use a water-based lubricant unless the product says otherwise. Silicone lubricant degrades silicone toys — the two do not go together, however good each is on its own.
Cleaning and storage
Warm water and unscented soap after every use, dried fully, stored apart from other products rather than in a drawer with them. Silicone left touching some plastics will mark.
If you are choosing between two specific products, the contact page reaches someone who will answer straight.