While they are both intended as family permits, the K3 Visa for Spouse and the IR1 Visa grant different benefits to their holders.
The K3 Visa is a temporary permit with nonimmigrant intents. In other words, it grants only a limited authorized stay in the U.S.
If you wish to spend more time in the country and get a Green Card, you should apply for an adjustment of status.
While on a K3 Visa, you can travel freely outside the U.S. However, if your marriage ends before you can get a Green Card, you must leave the country within 30 days. Additionally, you will be allowed to work in the U.S. only after applying for a work permit.
On the other hand, both the IR1 Visa category and the CRI1 Visa process have immigrant intents. This means that, together with your visa, you will be granted a conditional legal permanent status. As a CR1 or IR1 Visa holder, you can seek employment in the U.S. without applying for a work permit.
It must be noted that both visa application processes begin when your U.S. sponsor files a Form I-130. However, if you wish to apply for a K3 Visa, you must also submit a Form I-129 to the USCIS. Moreover, you may need to file ad affidavit of support for both visas, to show that you do not intend to rely on the U.S. public financial support.