To be honest, I've used Instantly, Sales Forge and a few other email sending softwares. No opinion on Clay sequencer coz I've never used it.
If you want to do multi-channel outreach (LI + email) and need a bunch of workspaces for different client's - take Sales Forge
If you just need to send emails and need 1 workspace - take instantly.
It's cheaper and more convenient if you are doing multi-channel and have to do it for a bunch of client's.
PS - also, beware's instantly's really slow support (in my experience at least. Sales Forge's has the fastest support I've ever seen in any email sending tool - even on a Sunday lol)
