I have a variety of formations I use in different situations.
Standard is 4-3-3:
------------Guzan----------- (Rui Patricio against abnormally quick teams)
--------Palmieri-Sariw------- (Sariw is Offense Priority & a good shot, so he's perfect for CB Overlap)
Virota------------------Wome (Balanced --- Offense Priority)
----------------------------
---------------BAL---------- (My now 106-rated character, DMF, Balanced)
--Tolchotryzn--------------- (Usually CMF, Balanced)
----------------------------
------------Hamsik---------- (CMF, Offense Priority and Free Roaming card enabled)
----------------------------
--Arnautovic or Muniain------ (SS)
----------------Sturridge--- (SS)
----------------------------
------------Foti------------ (CF)
When attempting to hold a lead in a tight game, I'll switch to 4-5-1 or 5-4-1 with 2xDMF + CMF or AMF and 2x DF Priority SMF, employing Miruic (6'8") as the lone striker.
If I need more balance, or if the opposing team plays with a very narrow formation, I'll use a 4-4-2 with a fairly deep-lying DMF + CMF pairing (usually the DMF with DF Priority, the CMF Balanced), two SMFs, and typically a big man/little man combo in attack, unless the opposition defense is physically strong, in which case I'll use two big, "true" CFs.
One of the most important aspects of my team is having a variety of fullbacks. I have three natural RBs and four natural LBs, all with different qualities, which lets me adjust my defense to the opposition. If I use Cejumi and Wome, I'll have tons of offensive support and pace to cover their forays forward, while choosing El Moubarki and reborn Mitchell Pique gives me durability, resilience in marking, and excellent defensive cover. The others are somewhere in-between (my first choice, Virota, is extremely powerful and well-balanced), and/or offer useful perks (Corrales can play on both flanks as SB, WB, SMF, as well as CB and CMF, while Cordeiro is a tricky dribbler and fantastic crosser). The right complement of fullbacks greatly facilitates the breaking down and/or just plain shutting down of any opposing formation.