I have two and there's a big gap (5 years) between them. I don't regret her at all, but there are definitely moments where I'm conscious of how life is more difficult now than it would be otherwise. Eldest is nearly 9, and when I speak with friends who have similarly aged children, there's a sense of more independence for the children, and more freedom for the adults, as they're able to do more non-parenting things as the child gets older.
My daughters are also quite different in personality, oldest is more easygoing, youngest is quite strong willed. Parenting her feels relentless in a way that I hadn't anticipated, and the exhaustion can be hard going. In having a second with a big gap we've stretched out the early parenthood exhaustion over a longer period, and it's hard. But on the other hand, they're so lovely together and watching my eldest be a loving big sister is so worthwhile.
The other thing is, parenting's a long game. It's incredibly hard work now, and there are times when it's frustrating that they're at different ages and stages, but they're not little children for long. Our relationship will grow and change as they grow, they'll become teens and then adults and having the bond between them, as well as the bond they have with us, is part of what I wanted from a family. Like @MaltipooMama says, the thought that they have someone in their life who knows them and shares their history is a great thing, and I hope they can be a loving and supportive presence to each other when I'm gone.