Currently I have 2 apks (64bit and 32bit) to upload on playstore. So I would like to know which method is better for doing upload-APK or Bundle.
Use App Bundle if you are uploading your apk to the playstore.
People have managed to reduce almost 50% of the app size even after the heavy optimization. You don't have to suffer the app quality also while doing so. Plus, google has now started to give you a warning if you don't upload the app bundle and use the apk instead.
App Bundle is actually a bundle that consists a set of your APKs. Read more here