Basically there are three types available; paper; electronic; computer based. I find that I use all three. Paper ones are very useful but can be bulky to carry about and take time to search through. Electronic dictionaries are very convenient, can be carried about but can be expensive and complex to use. Computer based dictionaries have the speed of an electronic dictionary and can be much cheaper (if you already own a computer) but even on a laptop they are not exactly portable.
It is well worth having a couple of dictionaries. I’m surprised by some differences there can be sometimes in definitions and translations. So far JEDict is my favorite. However my Canon G55 is growing on me.