[Les Meehan]

Bellows are the more flexible (pun intended) option since they give you continuous magnification changes so you can get exactly the image magnification you want. The tubes, being fixed length (sets of 3 tubes), provide a more limited option.

However, bellows (especially automatic ones) are usually much more expensive than tubes and are usually bulkier. Also, I would recommend a focusing rail which allows you to set the magnification and then move the entire camera setup forward and back on a tripod without upsetting the magnification. Most good bellows will have this rail built-in.

Auto-tubes are usually a good buy for the occasional foray into macro or a macro lens may suit better.

Depending on what type of subject matter you want to shoot, an alternative is to buy manual bellows (cheaper than auto ones) and a good quality enlarger lens/adapter to fit the bellows. Enlarger lenses (which are peanuts on ebay now) are designed for close work and may actually produce sharper results than your usual lenses (if not macro lenses).

The other usual advice if using a normal camera lens for macro is to reverse mount it on the tubes of bellows (there are usually adapters for doing this and retaining the auto features of the lens). I won't bore you with the technical reasons for this (unless you already know of course) but it produces sharper results.

Cheers

Les