Honestly depends on what you're going for. Suicune is generally running 2 different EV spreads - 252 HP / 252 Def / 4 SpD, and 4 HP / 252 SpA / 252 Spe.
The first EV spread is used for the infamous CroCune, which is the Rest / Sleep Talk / Calm Mind / Scald. The moveset works because of Suicune's great overall bulk and access to Pressure, PP stalling the opponent. The other use of this EV spread is a phazer, with the same set as above but Roar over Calm Mind.
The second EV spread is used on offensive variants, generally a Calm Mind / Hydro Pump / Ice Beam / Hidden Power. Suicune has decent offensive stats, although its speed is a bit low.
So if you're looking for a more defensive Suicune go with the first one, otherwise use the second one.