How do I check a value when creating new content? My rule fires after saving new content. The first condition to configure has to be entity is of bundle Src. I don't know how to setup this condition correctly. I chose Entity:node, Type: MY_CONTENT_TYPE, Bundle:Default. Which doesn't work.

What would I have to enter to make this work using the Rules module?
You should try to use the "entity has field" Rules Condition (instead of entity is of bundle). In my experience that one works to make that field available as a token in subsequent Rules Conditions and Rules Actions.

If you have other reasons why you need to add that entity is of bundle condition also (I doubt, but one never knows ...), that's fine too, but make sure to do so only after the "Entity has field" Rules Condition.

Refer to the answer to "How to specify a Rules condition related to select list values?" for an example rule.

If you're not familiar (enough/yet) with Rules, checkout the 32 (!!!) great, and free, video tutorials Learn the Rules framework.

PS: I'm assuming this question is about D7 ...