moxfactor

我個人認為extension tube會比較好啲, 主要因素係因為始終少塊鏡.  第一係最簡單, 少塊鏡少啲幾會有lens flare, 雜訊, 等等.  另外, 鏡頭同機身接駁位同鏡面/filter面鏍絲位比較起上嚟, 應該係機身接駁位比較耐用, 而且裝上/拆除比較容易, 當然, prot/uv filter比例上係唔值錢, 但係如果你有試過filter駁filter, 你就知道其實都幾煩, 鏍絲位亦好容易壞.  太緊難拆, 太鬆易跌.  如果同一支鏡有機會用嚟影唔同subject, 一時換close-up filter, 一時換grad. ND, 一時換CPL, 個filter ring唔壞致奇.  加上filter用多過一個(就算係一個厚身既prot/uv filter), 就好容易出現vignetting(黑角).  第三,  唔係賣廣告, 但Kenko套extension tube, 一套3個, 可以加上加.  close-up當然都可以, 但每多一個就多塊鏡片...多兩面機會黐塵...

以上為個人愚見~~

moxfactor

a longer tube will not affect vignette nor lens quality.

a thicker front element will affect vignette, depends on which lens you use and your subject matter, sometimes more than 1 piece of close up lens will be needed.
more glass will affect quality of photo, as well as additional possible lens flare(which if not facing the sun or a strong light source could be avoided with a lens hood) and chromatic aberration, which cannot be prevented.

i do agree that wider lenses should use close-up and good teles should use extension tubes, since the loss of maximum focal range from wider lenses render wider lenses inefficient.  if you intend to use a wide lens for macro, i can suggest a 3rd method, especially for inexpensive lens like 35mm or 50mm f1.8.  a reverse ring, where the ring screws onto the filter threading, and the lens with the reverse ring is attached to the camera with the front end of the lens towards the camera.  all controls will become manual, including f-stop, but it's quite easy to achieve beyond 1:1 ratio with almost no additional element or length.  however, manual focusing a reversed lens might take a while to get used to.

moxfactor

after researching more on the topic, i should change my statement that extension tubes will not affect vignette.  this is more correct...

an extension tube will affect vignette to a degree, but less horribly than multiple thick filter rings and cheap glass elements in front of the lens.  choosing "pro" filters will cut down on vignetting because of their thinner ring, but they're also fairly rare in variety, most shops in HK only carry "pro" filters for CPL and generic UV/protect.