It’s really up to you and which service meets your needs. Every service comes with its tradeoffs, so … if having data older than 5 years is important to you, then Garmin is less appealing … if sharing your accomplishments with others is important to you, then Strava is less appealing … That’s probably the biggest deciding factor for those two services.
The Garmin limitation has a workaround - request a GDPR export of all your data, then upload the FIT files to a separate service to get them into CityStrides … until I make time for Manual Upload anyway 