So! Let's see what color is worth pulling in the two banners for a free, random seasonal unit at 5*:
Banner 1
Red (25%)
Summer Leo (bad)
Halloween Nowi (sweet)
Winter Tharja (oh yeah)
New Years Camilla (eh)
Blue (12.5%)
Spring Lucina (bad)
Spring Xander (NASTY)
Bridal Caeda (eh)
Bridal Charlotte (eh)
Summer Robin (she has Lance Valor and is the only one with it so far)
Summer Corrin (eh)
Performing Shigure (decent because it's a singer)
Winter Robin (eh)
Green (9%)
Spring Chrom (eh)
Spring Camilla (good if you bother doing Gronraven+)
Summer Adult Tiki (has Axe Valor and is the only one with it so far)
Summer Xander (eh)
Summer Elise (has Green Tome Valor and is the only one with it so far)
Performing Inigo (decent because it's a dancer)
Performing Azura (sweet)
Halloween Henry (sweet)
Winter Lissa (oh yeah)
Winter Chrom (oh yeah)
New Years Azura (ooooooooh yeah)
Colorless (12.5%)
Bridal Lyn (sweet)
Bridal Cordelia (sweet)
Summer Frederick (bad)
Summer Gaius (bad, because Summer Noire is basically better)
Performing Olivia (decent because it's a dancer)
Halloween Sakura (has Dagger Valor, next to, ironically, Elise, who is also a seasonal)
Halloween Jacob (sweet)
New Years Takumi (eh)
Banner 2
Red (14.2%)
Bridal Tharja (sweet)
Summer Tana (sweet)
Summer Young Tiki (sweet, has Dragon Valor and is the only one with it so far)
Festive Micaiah (sweet)
Halloween Myrrh (sweet)
New Years Hrid (sweet)
New Years Gunnthra (sweet)
Blue (12.5%)
Valentine Lyn (sweet)
Spring Catria (sweet)
Bridal Ninian (sweet)
Summer Cordelia (sweet)
Summer Camilla (sweet)
Festive Ryoma (decent because it's a dancer and can be effective on armors)
Halloween Niles (sweet)
Winter Ephraim (oh yeah)
Green (10%)
Valentine Lilina (sweet)
Valentine Hector (oh yeah)
Spring Sharena (decent)
Spring Alphonse (decent)
Bridal Sanaki (sweet)
Summer Innes (decent)
Festive Elincia (decent, but then again, she's currently in the Mythic Banner)
Halloween Kagero (sweet)
Winter Fae (oh yeah)
New Years Fjorm (decent)
Colorless (11%)
Valentine Roy (decent, has Bow Valor, but so does Nina)
Spring Kagero (decent)
Summer Noire (decent)
Summer Linde (decent)
Festive Xander (decent since it's a dancer)
Summer Takumi (sweet)
Halloween Mia (sweet, only other staff flier next to HS!Sakura)
Winter Eirika (sweet, only armored staff unit)
New Years Laevatein (decent)
Personal Opinion:
On the first banner, it's a very loose canon. You can be really screwed up and only come out with something decent. Green has the best units. Colorless is risky, as it has very good units...next to really bad ones.
On the second banner... Hoo boy. Look at Red. Full of many good picks. The other three are equally decent.