It depends on what you're looking at. The Omega gear has item sets, which are in general more powerful than non-set items. However, its selection is rather limited to mostly Borg-derived and anti-Borg equipment. Except for the item sets, if you're not fighting Borg day in and day out, you're better off with Fleet gear.
As far as I know, though, the MACO shield is still the best in the game.
Stick with the fleet gear! It's better and cheaper!
No, its not.
Weapons, yes but that is because STFs weapons were removed but sets? no way in hell. And you be paying its weight in Dilithium anyway so why waste it in Ship equipment when it not going to beat the sets.
Ground is even more lopsided since sets give powers, like MACO that comes with a buildin shield recharger so if you are not playing a Eng you get a Shield recharging ability for free, not even mentioning the passive abilities that Fleet Ground gear will lack.
Outside Ship weapons, you go with the Omega Store if you can.
Some of the elite fleet pieces have fake set bonuses built in - the shields have an adaptation proc that's almost identical to the Aegis 3 piece set. Any kind of split setup with an off-set shield would do well with an elite fleet shield. The standard fleet shields not so much, they just have random collections of resistances and no adaptive resistance.
Fleet gear is arguably as good as (perhaps better) and Set gear piece per piece.
Set gear does have an advantage over. They provide 2 and 3 piece set abilities. Those extra abilities don't take up a gear ot device slots. It's nice to have an extra Shield heal, health heal, or defense boost when devices are on cool down.