Unless you like women's tennis, then you absolutely have to have Sky Sports.
They cover all the Master's Series, plus Davis Cup ( not Britain as that's on the Beeb) and the US Open with multi choice screens on most of those tournaments.
I loathe EuroSport. They are patchy in their coverage, although they do cover ATP Gold and International Tournaments, but when and who is a real lottery.
The downside of Sky is having to listen to Barry Cowan and Sam Smith. Cowan brings a new meaning to banality, so invest in ear plugs.
It's not cheap, but it IS the best.