Don't get an SP1 - you can't get parts as the guns are no longer made. Always buy a gun you can get parts/accessories for easily.
If the choice is just the Tango or the P98, the only difference is the look, and the ACT. The Tango does not have the ACT, but you can choose the front grip. You are stuck with the stock front grip on the P98, which is uncool.
Personally, if I had to choose and couldn't get an A5 instead, I would choose the Tango. Then I would put a Cyclone feed on it with low-profile hopper, and a folding CQB grip, plus a folding/car stock. Then I would put an e-grip on it, and a Lapco Bigshot Assault barrel. I would of course have spent more on it by now than if I had bought an A5 with egrip......