Well here in italy nothing can be done without an interface. This is a silly market where companies keep selling domains at $2/month getting thousands of customers a month.
We've experienced DI's panel and it looks like terrific, then we've got Plesk very basical I must say.
Sphera is very good but price is $400/month (yes $4/month but with a thresold of 100 Vservers).
Alabanza's one is (was) very nice to handle but .. oh well lots of things have been written about it.
Now we are happy (and I mean HAPPY) using VDI (at UltraspeedUSA getting a SUPERIOR support), this is upgraded frequently and allow our resellers to perfectly handle new domains.
So I guess it really depends on the market you are running on.