I've tried several prepaid SIMs recently, and honestly, choosing the right one can be quite confusing. Some are available at convenience stores, while others can only be ordered online. Also, the speed varies quite a bit depending on the time of day.

HIS Mobile's prepaid plan stands out with unlimited data for 30 days at around 3,500 yen—an incredible deal. It can handle videos reasonably well, making it the best value for everyday use. However, during peak hours, speeds drop to about 6 Mbps. Still, browsing websites isn't an issue. The only downside is that it's only available through online orders.

Nippon SIM for Japan offers a large 50GB plan for 4,480 yen for 30 days. It's easy to set up—just insert and start using it immediately. It's also sold at electronics retail stores, which is helpful if you need it urgently. But, the speed during the day isn't great.

If you want to buy and start using a SIM immediately at a convenience store, the only option is IIJmio. You can find it at Lawson and Mini Stop. With eSIM, you can start using it in just 5 minutes. However, the price is higher—10GB costs 3,280 yen.

For speed-focused users, Parrot Beak's JAPAN PREPAID SIM is a good choice. It uses SoftBank's direct network, so it's stable and reliable. Even during congestion, it remains comfortable to use. 10GB costs 2,380 yen, which is affordable. But 50GB costs 6,480 yen, which is quite expensive.

Ultimately, it depends on what you prioritize—cost, speed, or purchase method. Prepaid SIMs require balancing price, speed, and convenience. If you need it immediately at a convenience store, options are limited. If you're okay with ordering online, look for cheaper plans with larger data allowances. Choosing based on your usage style is the best approach.