The Explorer 1 model usually has a dial diameter of 36 mm, while the Explorer 2 model has a dial diameter of 40 mm, which means that Explorer 1 is more suitable for people who like smaller dials, while Explorer 2 is more suitable for people who like larger dials.
Choosing 36 or 40 mainly depends on personal preference and wrist size. If you like a small and exquisite dial or a thin wrist, then 36mm Explorer 1 may be more suitable for you. If you like a bigger and more eye-catching dial or a thicker wrist, then 40 mm Explorer 2 may be more suitable for you.
In short, choose 36 or 40, depending on personal preference and wrist size. You can try on two models in the shop to determine which one suits you better.