no matter how impeccable your rdns, spf, dkim and dmarc configuration is, even if you're an absolute master of configuring postfix and opendkim, etc, your outbound smtp deliverability success rate is going to be very much dependent on the reputation of your IP space.
the best possible IP space will be somewhere that the entire /24 and parent /22 or larger block does not belong to anybody else's low cost VPS, VM, dedicated server or shared hosting. Which is hard to find these days unless you personally know somebody at a mid sized regional ISP that can sell you a custom package of colocation and some small sized piece of public IP space (like a /28 or /29 for your server) in known clean IP ranges.
the best possible IP space will be somewhere that the entire /24 and parent /22 or larger block does not belong to anybody else's low cost VPS, VM, dedicated server or shared hosting. Which is hard to find these days unless you personally know somebody at a mid sized regional ISP that can sell you a custom package of colocation and some small sized piece of public IP space (like a /28 or /29 for your server) in known clean IP ranges.