I think that Adobe InDesign is indeed the best program to create print ads. Because it has a lot of typographic functionality, language support, can use raster images and vectors and is able (when you use rgb images) to create output for different output color spaces as it is needed when you want to create print ads for different magazines in different countries.
But you have to learn a lot to use it properly.
More than half my business is advertising, and I do it all in InDesign. You could do individual ads in Illustrator, or even Photoshop (I worked for a newspaper once that only had Pagemaker and Photoshop, and my predecessor had created all of her ads in Photoshop), but my preference is for ID.
Forgot to mention that if you do an ad in photoshop you want to keep the various vector and type objects live and save as PDF, NOT .psd.