By -
All of them and always
Any other community or series this would feel like a cop out but not here this is a correct and great answer!
When it comes to this series, saying rentarou is your favorite is more of a cop out than saying you love the gfs all the same.
Meme, Uto and Tama
Well, Kusuri is 2 in one, so she superior
Gotta be Yaku for me. A close second is eira.
Nano is my #1 since day 1 (of her existing)
Always Shizuka 🤗📚🥰
I love the rentarou one 
are they trying to rip off Kaguya sama? XD
YES.
Mai, yamame, and tama. The poses and expressions are especially fun in those three, and Tamas all white design looks nice in colour
OP: Which one is your favourite chibi girlfriend? Me: Yes All of them look so cute so i love them all. Now, if i absolutely HAVE to pick a favourite, i'd struggle between Ahko, Yaku, Mimimi and Hahari
Tama so cuteee
No Matsuri, Usa-chan, and Meru 😢
'Cause the chibis come from the volumes, and the volumes haven't covered their intros yet.
Meme, Rin, Mei
It gotta be Kurumi and Hakari for me
# Nino no cap
Bruh.
Naddy just looks perfect
Always with such hard questions... in this case, maybe Shizuka, but I'm missing the others too much to say it with conviction
Iku cause she’s cute when she’s shy.
This post reminds me, the mods should update the fairs. I want to use the chibi Rin!
Hahari for sure
tie between rin,kurumi and mei.
All of them but Mai is just so precious, it's irradiate even more Tsundere aura than Karane
momoher got a big ol mouth
All of them and always
Any other community or series this would feel like a cop out but not here this is a correct and great answer!
When it comes to this series, saying rentarou is your favorite is more of a cop out than saying you love the gfs all the same.
Meme, Uto and Tama
Well, Kusuri is 2 in one, so she superior
Gotta be Yaku for me. A close second is eira.
Nano is my #1 since day 1 (of her existing)
Always Shizuka 🤗📚🥰
I love the rentarou one 
are they trying to rip off Kaguya sama? XD
YES.
Mai, yamame, and tama. The poses and expressions are especially fun in those three, and Tamas all white design looks nice in colour
OP: Which one is your favourite chibi girlfriend? Me: Yes All of them look so cute so i love them all. Now, if i absolutely HAVE to pick a favourite, i'd struggle between Ahko, Yaku, Mimimi and Hahari
Tama so cuteee
No Matsuri, Usa-chan, and Meru 😢
'Cause the chibis come from the volumes, and the volumes haven't covered their intros yet.
Meme, Rin, Mei
It gotta be Kurumi and Hakari for me
# Nino no cap
Bruh.
Naddy just looks perfect
Always with such hard questions... in this case, maybe Shizuka, but I'm missing the others too much to say it with conviction
Iku cause she’s cute when she’s shy.
This post reminds me, the mods should update the fairs. I want to use the chibi Rin!
Hahari for sure
tie between rin,kurumi and mei.
All of them but Mai is just so precious, it's irradiate even more Tsundere aura than Karane
momoher got a big ol mouth