I started with two boys. I was looking for boys after my brother got a guinea pig when I was little and he eventually passed away. I always wanted another guinea pig after that and went out looking for piggies who looked similar (red eyed white) and I came upon a beautiful boar who I named Gilbert. I also got another boar from the same cage Ludwig, (they were the only two) and kept them together.
I then went and got another male guinea pig, Romano a year later and a few weeks after that, I got him a friend too.
I have since been through a few boys with Romano but have since recently gotten myself a female piggie roughly 2 months ago. She is lovely but in comparison to my boars, she is a lot less affectionate, a lot more skittish and not as into cuddles as my boys are.
The pros of boys are definitely to me, the bond I have with them. One of my piggies I affectionately nicknamed "my soul mate" and "my little shadow". This was Gilbert's boarfriend, Ludwig. He and I had a fantastic bond and he would follow me everywhere, preferring me to his own cage mate and I have another boy who is just as affectionate now called Matthew, but he and Romano have an equally in love bond as Matthew has with me.
Honestly boys are a bundle of joy and I would definitely get more if I could, which brings the downside.
Cons:
They can only be kept in two.
The struggle of bonding and fall outs.
As I mentioned, I have gone through many piggies for Romano, the first of which, Arthur, attacked Romano in a bloody fight over dominance when he was just over their 2 year anniversary and second, Corey who, though he didn't attack Romano, was a sexual pest and wouldn't stop chasing and ..... enjoying himself over Romano. He was happy to let Romano be the dominant, he was just a little excited over Romano which Romano didn't like.
Though I prefer boars, I am slowly switching over to girls because I do not have a lot of room and if I eventually want more guinea pigs, I know its more practical to have them all together or in just two cages. I'm happy with my current set up of 'bunkbeds' cages, with the bonded boars, Romano and Matthew on top and my neutered boar and wifepig at the bottom. If magically boys could be kept in more than duo's, I would probably stick to having boars.
I hope my rambles help somewhat.

; I tried not to go into a big story but I couldn't help it. ^^;