Until Mr. Laszlo answers, I'll throw my two cents in.
In general, one aspect ratio isn't more "professional" or more artistic than another. Many great compositions have been made over the decades in the 1.37 : 1 Academy ratio, more or less the same as TV's 4x3 ratio (1.33 : 1.)
Besides being an exercise in creativity as to choosing a frame to compose in, it's more of a marketplace issue as to which aspect ratio you need to work in. Theatrical projection has become mostly just either 1.85 "flat" or 2.35 "scope". Any digital project shot for theatrical projection has to take this into account, which is why 16x9 (1.78 ) has become more and more popular for people shooting video with the hopes of a theatrical release.
Broadcast TV / cable has been 4x3 (1.33) for decades but is moving towards 16x9 widescreen (1.78 ). Some shows are shot in 16x9 (either in film or video) and the networks are broadcasting them in 4x3 with a letterbox to preserve the 1.78 image; but others will crop or pan & scan to show 4x3 full-frame. So it's a bit of a confusing situation for TV in terms of what aspect ratio to compose for; you have to consult the TV distributor you are shooting for as to what they want. You may have to shoot 16x9 but "protect" for cropping on the sides down to 4x3.
As the TV market moves more and more into 16x9 broadcasting (especially for HDTV channels), then shooting programming in 4x3 could hurt future re-sellability. So I would say that in the long term, it would be better to invest in a film camera or video camera that can create high-quality 16x9 image. For 16mm, that means a Super-16 camera; for 35mm, it doesn't matter so much because the quality is so high that cropping to 16x9 isn't a problem but you could consider 3-perf, which is naturally 16x9; for video, it means a camera with a 16x9 CCD if possible.
