favourable : 普通用词，指预示从良好的结果中能得到明显好处，有利于达到目的。
- It's believed the conditions in which the elections are being held are too favourable to the government.
fortunate : 指目前已存在的成功或有利情况，或指因好运或机会带来的成功和喜悦。
- You're very fortunate to have found such a nice house.
- He was fortunate in his choice of assistant.
- It was fortunate that they had set out early because the traffic was terrible.
happy : 侧重指不是通过某种机会，而是凭借鉴另和选择手段而得到利益与好处。有时也指偶然得到的好处，但强调的是有利的结果。
- We hadn't planned to be in France at the same time as Ann and Charles - it was just a happy coincidence.
lucky : 多指偶然机遇中的有利或幸运情况。
- "I'm going to Japan." "Lucky you!"
- The lucky winner will be able to choose from three different holidays.
- They're lucky to have such a nice office to work in.
- He's lucky that he wasn't fired.
- It sounds as if you had a lucky escape (= by good chance you were able to avoid something dangerous or unpleasant).
- We'll be lucky if we get there by midnight at this rate (= we might get there by midnight or it might be later).