Is it better to update to macOS Monterey or macOS Mojave?

If your Mac is capable of running either, the decision may boil down to which is more important to you:

• Compatibility with 32-bit applications, or
• Compatibility with current commercial applications (such as those from Adobe and Microsoft)

That depends on the Macbook Pro's sub-model, which you have not shared. You must have a 2012 or newer model to upgrade to Mojave, and an Early 2015 or newer to upgrade to Monterey.

Please do "About this Mac.." from your Apple menu and tell us what that shows for SUB-MODEL. Example:

For security reasons, please DO NOT post your serial number here.

FWIW, you need one of these Macs to install Monterey…

macOS Monterey is compatible with these computers - Apple Support