Photo from chessbase.com
The 4th round game 3 of Alekseev - Aronian show a good example of ending with two bishops against two knights ending. Modern players prefer the two bishops for the very good reason that they tend to win games. Usually the two bishop are better in more positions than not. This is because the main disadvantage of the lone bishop, its inability to control squares of a particular colour is nullified by the presence of the other one. This factor makes the two bishop so strong in open position!
However, the side with the two bishops have to be carefull to avoid exchanging one of his bishop because the endgame of knight against bishop is totally different. The lone bishop will having certain problem because it's path is limited to only the squares of his colour.
In blocked positions, the knights can offer tough resistance especially if they have unchallenge anchor squares. The knights can even be superior in blocked positions where they have outposts and the bishop's scope is limited.
Jakovenko,D (2710) - Aronian ,L (2741) [C88]
World Cup Khanty-Mansiysk RUS (4.3), 05.12.2007
This is the position after move 33
32.f4 h5 33.Nge2 Kf7 34.Kf2 Bf6 35.Nf3 Ke6 36.Ned4+ Kd6 37.Ne2 37...Bd5 38.Ke3 Bd8 39.g3 Bb6+ 40.Nfd4 Bg2? 41.c4 bxc4 42.dxc4 Ba7 43.Nc3 43...Kd7 44.h4 Bf1 45.c5 a5 46.Ncb5 Bxb5 47.Nxb5 Bb8 48.Kd3 axb4 49.Kc4 Ke6 50.Nd4+ Kd7 51.Kxb4 Bc7 52.Kb5 Bd8 53.Nf3 Kc7 54.Ne5 Bf6 55.c6 Be7 56.Nxg6 Ba3 57.Ne5 Bb2 58.Nf7 Bd4 59.Nh6 Bg1 60.Nxf5 Bf2 61.Ng7 Bxg3 62.Nxh5 Bxh4 63.Kc5 Kd8 64.Kd6 Be1 65.Nf6 Bb4+ 66.Ke6 1-0