Here's another way to look at ABC vs. the others, because it's dependent partially on what your situation is. ABC is definitely more comprehensive, but the more comprehensive the dictionary the greater the likelihood that you'll run into terms that aren't in common use. i.e. if you attempt to use one of those words someone will look at you funny because they don't understand. While ABC is an excellent dictionary it fits into this category. The great thing about ABC is it does have all sorts of uncommon words that you will run into if you're actually interacting with people in China.
The strengths of the Oxford dictionaries is they only focus on words that are actually in common use - I find when I actually reference Oxford I rarely find myself in a position where I used the wrong word.
For 1.0 the most comprehensive English-Chinese dictionary is the free LDC dictionary, however this dictionary definitely includes a lot of terms that are not in modern use, at least in mainland China - you'd actually be better off not using ABC when you cross reference it. Cross-referencing LDC with Oxford should keep you from utilizing a word that you shouldn't, while ABC might mislead you.
The other free dictionaries are also good for commonly used words, Adso is pretty comprehensive and CEDICT is nice just because it keeps the translations short and sweet.
Bottom line, if you're in actually doing your study in China then the ABC would be most useful. If you're planning on studying on your own at home then you can go quite a ways with Basic + the free dictionaries.