Best AI Services for Writing Email Intros with Apollo Integration

Hey All, might be a basic Q, but I'm getting started with using AI to write first lines of emails - I would like to draft lines based on basic enrichment from Apollo ie. contact location, etc. I'd like to hook up via API to save credits. -What service ie. GPT, Anthropic, etc. is recommended these days? -I haven't done a deep dive, but it seems like there are some barriers to getting an Anthropic API key (and i'm getting errors attempting to hook up my GPT key). Any recs based on this? Thanks