Two points:
1. I consider benevolent aliens more likely than malevolent ones - if they survived long enough to develop means of interstellar travel, they will probably have learned their lessons in civilized behaviour and respect towards other life forms. Also, whichever resources they may want are more easily found elsewhere, so they will avoid "native trouble" with us. They will thus not kill or plunder us, but they will study us - civilizations are probably rare enough to render us an interesting object of study (provided they are as curious as we are - but if they are not curious, they won't have science, and if they don't have science, they won't be able to reach us). Yet, of course, that they don't mean to harm us doesn't mean that they don't do any harm.
2. No matter how often first contact scenarios have been rehearsed in science fiction and UFO folklore, I doubt that we are really equipped for it and will keep calm and carry on when it actually happens. It will be a major cultural shock, and people will go crazy about it in every imaginable way. There will be trouble, but the troublemakers probably won't be the aliens.
To summarize: they will most likely come in peace, but nevertheless will provide for major drama.