I always opt for a team over single "specialists".The problem with using a single tester on a dedicated project is that the test can sometimes get tunnel vision because they've been down the same road so often. Generally you'll see cycles begin to be executed more quickly, which is sometimes and indication that the work isn't being done as thoroughly as it once was.
Getting a fresh set of eyes on it periodically can be a huge help and will also expose new, different bugs that the specialist didn't find. So working in a team allows for this flexibility.
9 out of 10 people I prove wrong agree that I'm right. The other person is my wife.
Adding on Brent's comments, when you work on a team of engineers who specialize on testing you have a better chance to improve your testing skills by sharing knowledge and experience.
There are multiple other advantages ranging from the ability to add extra resources when needed and all the way to having a bit more muscle on the political game, but in short I would go for the separate team.
Picking up on what the boys have said I can see where they're coming from, but I do still not quite understand where YOU are coming from.
At face value however and picking up from the others comments, I start by saying I think that it depends on some answers to some key questions
How does SDLC work in your organisation?
What development strategy do you employ?
How complex are your system(s)?
How does your organisational chart reflect SDLC?
How much domain expertise do you have in your team?
Are your delivery dates flexible?
Time to Market driven?
An Agile team might be more weighted to a single tester versus a traditional waterfall method requiring more team oriented testing.
In general, as with my esteemed colleagues, I would definitely opt for the team approach, but as with most organisations its not a once size fits all answer.