Get Earth Eagle/Aquila, it is pretty much top tier uncustomised, all of it's parts are useful.
Poison Serpent is bad, only has one useful part, SD, which can be obtained by the more useful Dark Bull.
Storm Capricorne is terrible, no useful parts.
Dark Cancer and Burn Fireblaze have one useful part each (CH120 and Burn), though Cancer is a good clear wheel while SF can be used for destabilising purposes.
So, Earth Eagle should be your first choice, followed by Dark Cancer. Third choice should be Burn Fireblaze and I would recommend not getting Serpent and Capricorne.
Poison Serpent is bad, only has one useful part, SD, which can be obtained by the more useful Dark Bull.
Storm Capricorne is terrible, no useful parts.
Dark Cancer and Burn Fireblaze have one useful part each (CH120 and Burn), though Cancer is a good clear wheel while SF can be used for destabilising purposes.
So, Earth Eagle should be your first choice, followed by Dark Cancer. Third choice should be Burn Fireblaze and I would recommend not getting Serpent and Capricorne.