Next season I don't know. But right now, 3-5-2 is a good solution. I like 4-3-3 more but I think right now we are not very suited. Because we don't have enough creative players upfront. Whilst 3-5-2 reinforces the wing play, making it possible to create more goal scoring opportunities with less requirement to wing players than 4-4-2 and 4-3-3 (the wingbacks in a 3-5-2 will have as much space to run forward as fullbacks but with less defensive tasks, unlike in a 4-3-3, the wing forwards/wingers have to have much more technique because they play more advanced and face tight defence constantly). It keeps the 3 center midfielders, which is our strong point, also because Pirlo is more suited to 3-CM formation. It also makes Vucinic closer to the goal.
Unless Elia can reach his potential and becomes our starting 11, replacing Pepe in a 4-3-3, I'd rather see 3-5-2 than watch Pepe in such an advanced position as a right wing forward in 4-3-3, without being able to dribble nor create much. Pepe is not good enough to play so advanced. His main distribute in attack is to run without the ball in scoring situations, which is not enough for a wing forward of 4-3-3, IMO.
The important thing is who you have on the pitch anyway. Is playing Pepe as a wing forward bettere than having Padoin as a wingback? Barcelona also plays with 3-men defence in many matches.