Most syringe tails are designed with finger rings, making it convenient for single-handed retraction, but syringe 2 is somewhat unconventional and less easy to use.

The tips of each syringe also look different. From an external view:

The design of syringe 1 allows the medication to fit tightly with the groove.However, it is not so easy to insert into the rubber, and this design also makes it difficult to retract.

Syringe 2 can be screwed into the rubber at the tail, but the downside of this design is that its groove does not match the medication.The entire syringe has a part that is suspended, which means the medication is not very stable. This is especially problematic during retraction, as the medication can be dispersed.

Syringe 3 has a design where the medication fits perfectly with the groove and can also be inserted into the rubber cap of the medication vial.

So after testing, syringes 3 and 4 are quite good. The above evaluation is for reference only.