Morning shinies
For me personally I like a pod mod kit as the pod tank is a lot more durable and tougher, than a mod with a subohm tank. Plus the 18650 pod mods are usually a lot shorter in profile and lighter.
A subohm tank probably gives you slightly better flavour from the same coils and has more capacity -so it's really a matter of what appeals to you.
In the 21700 pod mod category there was an explosion of them last year. The Oxva Velocity le is a brilliant kit for flavour, comes with a 510 and you can get the unipro RBA. I've also got Lost Vape's Ursa 21700 kit and that's just as good, except it's heavier. It comes with a 510 and the UB Pro RBA has RTA-like flavour. I wish Lost vape would bring that deck out as an rta.
As for the others,
@hittman and our other shiny reviewers are your best bet.