>good customer service

Discover and AmEx are most will known for this, but they may not be the best backup cards.

>no aggressive marketing email/telephone calls/mail

Avoid subprime lenders. I wouldn't call anything from my 6+ non-subprime cards overly aggressive.

>Ideally, looking for a card/issuer with a long billing cycle

All are required to give at least 21 days by law.

>if the issuer extends warranties for larger ticket items (e.g. computers/electronic devices) that would be awesome

This is becoming a rare benefit, especially on no annual fee cards.

You would be best off filling out the /r/creditcards template: https://www.reddit.com/r/CreditCards/wiki/cardtemplate