Choosing Between Clay and Instantly for Email Creation Efficiency

Question, for email creation, whats better, build the message in clay or directly in instantly?

In any case, Instantly or Clay, is it better to creare just the phrases/variables and add them to a template or it is better to create the full message?
I've used Clay with anthropic for full message with good results, but sometimes it doesn't work. Also spent credits.
Instantly has copilot + variables creation that would make more sense for me to create all the variables inside instantly instead of Clay for makeing it simple and for re-contact campaigns.
However, I've read many people talking about messging inside Clay. However it's more complicated to export a lot of variables from Clay to Instantly.

In overall, what do you think its better in the case of an agency that manage multiples customers (and simplicity is always worth).