Can I apply for a B1/B2 to return or is it best to stay here in the US until my I-130 finally gets an interview date in London?

You must have a valid immigration status to remain in the US while it is pending. This is determined by Form I-94. At 180 days of unlawful presence you begin to risk triggering a bar to reentry upon your exit. At 365 days of unlawful presence, the bar extends to 10 years.

If someone filed I-130 for you, you need to remain in London until you receive your immigrant visa. You may not come in to the US as a tourist while your I-130 is pending. Even if you happen to get this visa, you can be turned away at the border, once you get off the plane in the US. If you were already in the US on a visa, and then an I-130 was filed for you, and if your immigrant visa is immediately available, you could remain in the US (with some exceptions) to wait for your green card. But since you are out of the US now, you should remain in London until the process is finished.