I need advice om what to use my melters on.
I know that I should get them to 15,20,15 and expand as much as possible before using the melters.

I plan to use 1 on a ice with rings/ruins together with the two year award. Still far off.

Now for the last four the plan was to use them on four planets with rings/ruins. On the other hand could it be better to use the melters on planets with stealth screen as that would save valuable space, due to less cloak structures.

Ideally you would also use some QSE's to get them to Very Massive, giving you a Mega Colossal planet when melted.

In terms of what is better, I really couldn't say, maybe SS's?? Also don't forget Large moons, the extra space means for cloak and arti production too.

If your going to make it invisible, Go for rings/ruins. If you arent going to make it invisible, go for large moons

RT any viable SS planets that your using as project planets. The ultimate prize is a SS rings/ruins planet. A 22x MC can easily make over 3k AP without buffs when its properly built