Starting over with 350-500k contacts. Who to use?

Hi All!

We are looking to move our 350k active contacts off our current setup of about 10 years.

We currently have one brand set up on Maropost and Keap/Infusionsoft (350k active) and another with only about 20k contacts on Hubspot.

We love Hubspot but man is it pricey if we are looking to have roughly 500k contacts at some point.
We really want something that has impressive marketing deliverability, integrates well with Kajabi, has great list segmentation, and is cost-effective.

Sticking with Keap is a no, we tried Active Campaign for a hot second and it was a disaster.

So I am taking this to the experts! Would love to know your thoughts on Hubspot, Ontraport, GoHighLevel, and anything else you would recommend.

Thank you in advance!