If we beat Slovak Republic, we will face Switzerland and I wouldn't be surprised if both Federer and Wawrinka skip the tie, which would give us a quite easy win once again at home against Chiudinelli, Bohli and Lammer.
Federer has to play Davis Cup at least once by next year to be able to play the Olympics which is one of his main goals.
It would be better to play to have a chance to reach the world group than to avoid relegation to group II
Also the match against Portugal would be in Switzerland (right after Wimbledon) and not too tough on a fast court.
Actually I think the Swiss would prefer to play against the Portuguese because the Slovaks might play at home (would be decided by lot) and they might even play on clay