I'd recommend a medium-sized reseller account. However, if you were looking to add other sites onto your reseller package, you might want to spring for something larger. The great thing about reseller packages is that you can upgrade them without downtime
I will probably go down this path or a vps but has anyone got any larger mailing list sites as clients or run them themselves. I would be interested in hearing who they are using to host and what things they recommend look out for.
I am really happy with my host currently but they along with two other hosting companies got a bit scared at the size of the mailing list (which I didnt think was that big but anyway...). I was looking at getting a separate reseller account to what I have and just running this clients site solely on it but they were just interested in trying to sell me a dedicated server only.
I dont think the site requires a dedicated server. Apart from this lets say monthly newsletter it wont get that much traffic. I am prepared to pay a premium price for reliability and understanding of these issues and set it all up properly.