Depends what you need it for tbh.
If you want the actual sending infrastructure / API, I’d probably look at Twilio first for SMS + WhatsApp.
If you want more of a shared inbox / automation / CRM workflow setup for a team, respond.io is worth a look.
Main thing with WhatsApp though: it’s not really ideal for true cold outreach the same way SMS can be, because opt-in matters a lot more there.
So my take would be:
Twilio = infrastructure
respond.io = workflow layer
