It seems like Melanotan 1 has fewer side effects but needs to be injected more often and takes longer for your skin to tan. It's also currently being legalized in some countries for certain skin conditions, which means it has a bit of research behind it.
On the flip side Melanotan 2 has more side effects, but works faster. Almost magically fast. It doesn't appear it's currently being studied for possible legalization down the road, so there's less scientific research behind it, but it seems like most people either start with M2 or eventually switch to it.
What made you choose one or the other?