My male will live in a 20g tall for ever. My female hasnt dropped weight, and i am a firm believer that to big of tank is Bull Sh*t.
Well I'm sorry you feel that way. I don't think its a problem for adults, but I like to make things easier on my babies and have had three different instances where moving juvies into smaller enclosures seemed faired better. Many other breeders have had this experience as well- but I guess you know more since you're already on your second gecko and still asking no-brainer questions about their husbandry.
That kind of language is really uncalled for though.
I mean, you're asking which gecko should go in what tank when they're basically the same size and make no mention of quarantine methods. You say you've only had the female for a week, but want to know what tank to put her in. So unless she's been living out in the open for a week, you either put her in there already or you put her in with the male or you put her in a third tub and are already looking to move her again.
I'll keep in mind that I shouldn't try to go ahead and offer any bit of advice I think that can help make it easier for someone new to keeping geckos (and honestly, this kind of question means you're new or you simply don't care enough to read up more on their husbandry).