Both series feature a teenage girl who looks much younger than she really is and a guy who looks as old as the girl is suppose to be (but has a mind of a child). If you found that concept interesting, try the other series for more of the same.
Both revolve around a disabled couple (a bit more like sibilings in case of The Friendly Winter though). Both have drama and romance, though The Friendly Winter has better art. Although the series are different, if you liked one, there is no way you're not going to like the other one.
Those series are probably more different than they are similar, but something tells me that fans of one of them might find the other interesting. In both series the female lead doesn't look her age at all. Even though she is in her late teens, people mistake her for grade-schooler. Here comes the twist, in Toradora! the male lead (her peer) ends up having to take care of her (because she is kind of helpless on her own), but in Friendly Winter the guy (and he is 2 years younger than her) is the one who needs to be taken care of.