Do you use NPCs with PC levels?

No. 

I use statblocks and adjust them as needed. 

Had a DM before that built NPCs as if they were PCs.

Started it fine, but slowly became more and more of a problem, as he started seeing the npcs as *his* characters. 

Finally got to the point he saddled the party with an NPC "leader" who traveled with us,  but was 5 levels higher than us. 

It's faster and easier to just adjust statblocks, and less likely to get attached, imo

NPCs follow the same rules as PCs with every DM in our extended group.

And it is much faster to just create a character, than hunt and peck through hundreds of stat blocks hoping to find one "close enough" then having to go through the trouble of homebrewing it further. Just go into the character builder, and create the NPC.

Unfortunatley I have to keep all my NPCs in a separate campaign to prevent the players from seeing them, that's a bit of a pain, but better than trying to find a "close enough" stat block, then homebrewing it, then explaining to the group how there's 2 sets of rules to the universe, one that only applies to them, and one that applies to everything else - it strains credibility. The universe has one set of laws/physics/etc. and it applies to everyone.

Don't care if you disagree. Don't care if the Devs have moved so far from the way D&D was originally designed. Do as you wish at your table, but at ours every NPC has access to the exact same abilities as PCs. The PCs know what to expect, because their opponents follow the same rules that they do. That also means they can be counterspelled, just like a PC can be counterspelled.

I might use a couple of subclass features if I am feeling fancy, but the more mechanics I put on a PC, the more effort it takes to run. The more effort it takes to run, the less effort I can put in making the PCs shine. 

Since I'm the DM, I can improvise the NPC stat block having a class feature if I think it is appropriate.

I will use subclasses and feats as inspiration for humanoid-esque characters in the world. An example being the lower-level BBEG, Throwdown, who was an Ettin with the Polearm master/sentinel feats, armourer armour, and barbarian rage. I didn't bloat his statblock with artificer abilities (I just made him do then when it made sense) and focussed on making his statblock balanced with the rage and sentinel abilities. He has the fireball cantrip available to throw some ranged attacks out, but again, I didn't slow him down with mending and utility spells - combat only on the statblock, and if he needs to cast other ones, I decide if he has them!

I’m doing pirates so i use subclass and feats but have a chosen class so the enemy has stats if i make them bat an arcana role to recognise artificers arcane cannon for example as well as saving throws