I use cellphone apps for help when I first come to China, but most of them are machines-based, so sometimes the translation can be very strange, which bothers me a lot; I tried YesPo recently, it is much better than those I have been used. But I think it is also important for you to learn Chinese if you are going to stay in China for a long time.

Depends on if you want to learn some Chinese as well or just be lazy.

If you know some Chinese phrases and are looking for vocab filling (i.e. you want to buy a torch and don't know the word, but know how to ask for it) then I'd get K-Dict, it's free and works great with multiple words for explanation.

If you're lazy then get Google Translate, it works online only but can handle long sentences such as messages from your bank or the weather etc.

I personally use both, KDict for when I want to look up a single word and GT for when I'm translating a message and can't be bothered to work out what it says.

Some have recommended Pleco, this is great but it can get confusing sometimes if you're looking through all the definitions of a word. I'd get it and pay for the OCR which can use your phones camera to read a character/s on a newspaper, box, sign, wall, anywhere which is really useful in a restaurant that doesn't have pictures.

I'd stick away from most translators that claim to be free with advertising as they are just a front, they use Google's servers and push ads in your face, just get Google's native translator.