1.PilotHi-Tec-C: This is a very smooth neutral refill, with smooth writing, and it is not easy to jam or break ink. Its ink dries quickly and is suitable for daily writing and office work.

2.PentelEnerGel: This is another very popular neutral refill with excellent writing performance. It has good fluidity and stability, and is not easy to jam and leak ink.

3.Uni-ballSignoGel: This is a high-quality neutral refill with a smooth writing experience. Its ink dries quickly, is not easy to smudge, and is suitable for signature and meticulous writing tasks.

4. Sakura 18KGoldPencil: Although it is not a gel pen, the refill of this pencil is also very smooth. Its ink dries quickly and is not easy to fall off, so it is suitable for painting and detail description.

5.Zebra Saraseal: This is a very durable neutral refill with a smooth writing experience. Its ink dries quickly, is not easy to block and leak, and is suitable for long-term writing and office work.

Please note that everyone's writing habits and preferences are different, so it's best to choose a refill that suits you according to your own needs.