mine are 10 and 11 (13 months apart, a boy (older) and a girl). my relationship with my siblings has always been either negative or non-existent. as a result, i always, always said i only ever wanted one. but after my son was born we went to visit my husband's family. as i watched my husband with his brother talking about when they were kids, i knew right then and there that i wanted a second one ~ someone my son could not only spend but look back on his childhood with. before i knew it i was pregnant again, and my son was barely up on his feet when the second one came along. so, just like twins, these two have never really known life without each other, and they are extremely bonded to one another.

i definitely, definitely recommend two, and the closer in age the better. not only will they be more bonded to one another, but you will be able to resume the other parts of your life sooner, and you won't be running in two directions for the whole time they're in your house. they can enjoy a lot of the same things and keep a similar schedule if they are developmentally close to one another.

I recommend 2. It will ease the burden of caring for their aging parents.

I have two daughters, now 17 and 13.5 years old. And, I'm five months pregnant with baby #3.
I think it's been fabulous having two - they play well together, they squabble well together (learning conflict resolution skills that they then take out into other relationships), they help each other to learn (my younger one learned to read at age 3 by watching her big sister), they learn from each other's mistakes, so they only have to make half as many mistakes on their own for the same learning experience. They learn that other people have different likes, dislikes, priorities, and beliefs than they do. They learn about needing to compromise what they want in the moment for what the family as a whole needs.
I am glad that we had them 3.5 years apart. When I see people with a baby and a toddler, it just looks exhausting to me. More than I was up to handling at the time. (Although those parents say the benefit is that they have fewer years of their life in the baby and toddler stage).
It will be interesting to have baby #3, who will for much of his/her life be an "only child" as the big sisters will be away at college. Our goal is to help him/her gain the benefits of sibling-hood (conflict, compromise, understanding other people's perspectives) while also having some of the benefits of only-child life - more trips than we were able to take with two little ones, more one-on-one attention from the adults, etc.

The answer from my only child husband--- never have just one. It's lonely and not much fun.

Yes, two gives them someone to play with, someone to negotiate with, and someone to care for... and someone to make plans about whether to put you in an old folks home when you're old.

Just one aint enough, although it can be rewarding in itself, if you can let go of the appron strings.

Having the second child was one of the hardest decisions my husband and I made. Our first was super easy, very portable, and didn't actually make much of a dent in our lifestyle. But having 2 is HARD WORK, at least while they are little. My mother always said that one is easy, and having another is like having 5 more, and she was right. They are 3 years apart, and I can't imagine having them closer together - I can't take my eyes off the little one as he is pretty effing fearless. But from what I hear, it gets a lot easier as they get older.

Sooo - if health and finances are your biggest concerns: The first years of your second's life is an enormous energy drain, so I guess you have to factor that in to your overall health picture. Financially, the second is not a huge outlay of money provided you kept all the clothes and other crap from your first. If you're breastfeeding the first year, that saves a lot of money too. We don't pay for childcare though and don't really believe in paying for our kids college, so that saves us money.

But yeah, I would recommend 2. They are both so ready to be able to play with each other in a more interactive way - the little one's only 15 months, so he can't play legos with my 4 year old and my 4 year old can't do the piledrivers on the baby with full force quite yet, but in two years they should be playing together quite nicely and staying out of my hair.

I'm a younger sister too, and I can't imagine my life without my older sister.

I am an only child myself, and although there are good things about it, and as others have pointed out, some people seem to get absolutely no joy from their siblings, I think at times being an only child can be lonely and isolating. (Wait, is that the smallest violin in the world I hear?)

I am finding as my parents grow older and a little forgetful I am the only person who remembers a lot of little details about our life as a family unit, and that makes me kind of sad. How could they forget the time my father caught the falling aspic in a fancy restaurant?

It sounds like some kind of breeder propaganda, and of course you have to pay twice as much for daycare, but I really beleive two is easier, for all the reasons other answerers have mentioned. I have two, and although they sometimes scrap with each other, I have observed that they genuinely love each other and their lives are enriched by each others companionship.

Most childrearing experts agree, though, that three years between siblings is ideal, that way there is no competition for the kind of intense care and attention that babies need.

Well, actually we have 4! Your question causes me to suspect you may be an only child or first born. If so, your experience of either having unlimited adult attention or being 'dethroned' makes having more than one child feel daunting. The image I like to share is that of a candle flame. If each flame represents 'all our love', as we add candles, the love keeps growing and getting brighter. And so do families.