Planning on getting a 2nd dog when our 9 month lab is older. Not sure if all rescues insist on resident dogs being neutered (our small local one does) if they do we'll get a puppy but would love a 1 - 2 yr old staffie. We've decided not to get our dog done, vet's opinion is that we shouldn't unless there are behaviour problems. We've thought a lot about it and want to do the right thing, health wise there seem to be more cons than pros for male dogs, and we meet lots of friendly obedient labs of all ages on walks that haven't been neutered and owners say they haven't had any problems.
I think if you were planning on getting a staffy, you'd be better to go fo a bitch seeing as your lab is a male. It's not universal, but one breed trait of Staffies can be same sex dog aggression or a tendancy to it, and with any breed/s one bitch and one dog are less likely to encounter problems getting along than two dogs or two bitches. So, even if you get a puppy, you may need to look at neutering anyway.
I am the absolute last person to neuter my own dogs without any reason and I would personally never neuter early, but if you allow your dog to mature, the negatives to neutering him are much less and it's a fairly minor op for a dog as opposed to an invasive one for a bitch. However, it is something I would consider in your situation and as it would best to wait until you lab is around 2 years old before getting another dog anyway, your lab will be fully grown and a good age to neuter by then.