I have 4. 2 are married to my brothers. 2 are my husband's sisters. I love them all, but am actually much more social and "hands on" with my husband's sisters. We are just closer somehow.
My oldest brother's wife is older than me and they were married and had children before I even was thinking about marriage--- so we didn't bond that well, as my head was totally somewhere else from hers. And they lived 6 hours away from me so it wasn't like we saw each other often. We were in very different places in our lives, and it seems we have maintained that.. ummm... distance(?)...
My middle brother didn't get married until a few years ago.. She is younger than me (by almost 10 years) and they (to date) have no children. So we have little in common, including life experiences in general... and they too live many hours from us.
My husband's sisters, however, are slightly younger than me, and I found them very open and fun, and very much wanting to have a good relationship with me. They much admire their older brother (my husband) and have turned to him (and to me, by default) over the years for advice, companionship, an ear, etc. Something that my brother's wives have not done, or not felt the need to do. ALL of my SIL's fathers are deceased. Which is an odd little bit of information to throw into the mix. 2 by cancer over 10 years ago (my brother's wife's dads) and my hubby's step-dad about 4 years ago (Lewie Body disease, after misdiagnoses of both Parkinson's and Alzheimers).
I do not always agree with what my hubby's sisters have done in certain circumstances, but I think they have always tried to do the best they could in their particular circumstances. And they are lots of fun to be around---very quick witted and every visit/phone call has some sarcasm and bits of humor thrown into even the WORST of subjects. There is pretty much nothing off limits to have a joke made out of it. My brother's wives, on the other hand, are very sweet, but also seem a little reserved--as if they are putting on to be nice for their husband's family almost. Or just a little nervous to "let it all hang out". Usually when we are together, it includes the presence of our mom, and my SILs often seem a little not-quite-comfortable.... With my husband's sisters, their mom isn't usually present at the same time, so maybe that is a part of it.
His family (in general, his sisters specifically) are not afraid to admit their problems and joke about hard times. My family is ever the "perfect" family and anything that is problematic is glossed over or whispered about. :/
So, my favorite things about them? first SIL- that she loves my brother unconditionally and they are a wonderful complement to each other, and she has raised 4 wonderful children with him, and can sometimes get under my mother's skin, (wink wink). most recent SIL- that she loves my brother and he loves her, and she is so laid back and relaxed with my brother. He is very laid back and dated some more "uptight" women--- she is adorable. It took him a lot of years to find her, and I am so glad he did. She lets him be a kid--which is a lot like my dad.
SIL via hubby: I just love hanging out with them really. I laugh more when they are around. We had my hubby's older sister and her family here to cook-out for Memorial Day, and I told her (while sitting outside with a glass of wine) that my face hurt from laughing and smiling so much that afternoon. And it was true. I just feel happier when they are around. They know a side of my husband that not everyone does (his mean evil devious jokester side-- totally smiling when I say that).
Wow- didn't mean to write a book!