I'll second the opinion on AD. I also find it easy to get parts-- either samples or small quantity purchases from the Linear Tech Web site. If the web site will sell me 5 pieces at a reasonable cost plus shipping, I see no need to bug them for free samples.
I've also upgraded my opinion of Maxim in the last year. I'm finding a better selection on the web site and have even been able to get small production quantities of some parts. They're not yet up to the level of AD or Linear, but the web site makes things a lot better than it was five years ago.
Mark Borgerson