I think it depends on your level. If you are a beginner or a low-intermediate students, an electronic dictionary might be convenient. You can take it with you and it's pretty easy to look up words. However, most of the electronic dictionaries that I have seen don't really give detailed information about a word. You can get basic meanings of words like "trend" or "spark", but you don't usually get a lot of "extras" like extended definitions, collocations, or idiomatic uses.
If you have a device like a iphone or something similar, there are really good dictionaries available. They are the same as very large books but conveniently electronic. And the internet itself has some good sites if you just need basic vocabulary meanings.