My favorite planet explosions were those in Star Blazers. They actually looked kind of like an exploding planet should look -- the crust breaking apart gradually as the expanding molten rock inside melts and cracks it, the whole process taking a long time. A planet is a huge thing and its destruction would be a slow, complicated process, not just a quick kaboom. The disintegration of the Genesis Planet in The Search for Spock has similar merits, although we don't actually see an explosion.
For the same reasons, I find the Alderaan explosion in Star Wars to be one of the stupidest ever -- it's just a jump cut from a shot of a planet to a shot of an ordinary liquid-fuel explosion. I get sick of the way virtually everything in Hollywood blows up with the characteristic fireball of a liquid-fuel explosion (which is not what most explosions look like in reality and is chosen because it's flashy, colorful, and not very powerful or dangerous as explosions go), but having a planet do it is particularly ridiculous, especially so quickly. And the Special Edition only made it worse by adding another entirely stupid explosion conceit, that of the impossibly 2-dimensional "shock wave" of light propagating outward. That conceit was probably inspired by footage of shock waves propagating outward along the ground from real, massive explosions, but a 2D "shock wave" in space is entirely idiotic both because space is 3-dimensional and because there's no such thing as a shock wave in vacuum.
