I have been working on a series of "10 Reasons To Visit..." articles. As things stand, they are currently limited to Malta and Sicily (with Sicily being 2 x 10 reasons because it's so great). I will add these to the relevant forums as and when I write more, but for now I hope you enjoy them: 10 Reasons To Visit... Malta 10 Reasons To Visit... Sicily (Part I) 10 Reasons To Visit... Sicily (Part II)
Anytime really, though I personally avoid the summer. It's a great winter break if you're looking for something good value and with probably the best weather you can find at that time of year without flying a long way.
We did Malta in June. It was nice but actually some areas are full of yob tourists and there aren't many beaches so as long as you know what you're going for you're fine. Valletta and Mdina are amazing and well worth the visit but Paceville is a bad area so avoid it there!