Fed Engineer was the first class I ran during the Open Beta, but I really disliked the emphasis on placeables. I went for science and tactical instead
During a promotion half-a-year ago, I recreated my old engineer character, and I noticed that there are enough kits to not have to put down generators and turrets anymore. What struck me was how much easier the content got with an engineer - most of the stuff going on past the Breen arc, especially the Heralds, end up hitting very hard. With a tactical captain, all you have are consumables. With a science captain, you have your health heals, but that comes only after your shields have dropped. Engineers have access to shield heals and consumables to recover health and they benefit greatly because restoring shields is a much less 'last minute' response to pressure.
As for space combat, while the tactical buffs really can't be beat as far as damage output goes, the engineers ability to reduce drains, up power levels and restore shields and hull on powers separate from the bridge officer powers comes in really handy. Or, at least, it's some of the most obviously beneficial profession-related abilities.
I have a Fed Sci (main), Fed Tac, Fed Eng, Rom Sci and KDF Eng in my stable of characters and I've played pretty consistently for the last five years (I'm probably the most active STO player on this forum). If anyone wants STO advice, just tag me here with any questions.