For me it's Flo's Notepad2
flos-freeware.ch/notepad2.html
It's Scintilla based without being a total piece of Scite. I say, I say, that's a joke son...
As a rule of thumb I dislike IDE's for the same reason I dislike a lot of more modern editors -- they try to shove everything into one window through tabbed interfaces; a massive step BACKWARDS in functionality if you're a multi-display user. It's nice to be able to open up three different files -- PHP, CSS, and JS for example -- side-by-side-by-side so I can see the code for all three and how they interact with each-other. It's just more productive that way.
Same goes for the stupid toolbar and panel bullshit that just sucks down screen space for nothing of value.. much like a lot of the artsy BS people crap into layouts wasting screen space on everything EXCEPT the content. In the case of many IDE's they waste screen space on pointless crap that would be better utilized to just SHOW ME THE HUFFING CODE!!!
Whilst there are a lot of editor features I like -- block level tabbing, indent rules, long-line rules, word-wrap indicators, tab to space / space to tab conversion, brace matching, multiple character set support, regex search and replace -- there are far more things slopped into 'modern' editors that just piss me off or get in the damned way.
Autocompletion is a great example of this, where most of the time I spend more time correcting or more time trying to figure out what the editor is doing for me, than I would if it just let me type the damned thing in! All I want to do is type some damned code, not jump through rings of fire because "wah wah, eye dunz wanna tiepz"
Colour syntax highlighting is something else that just pisses me off for being an illegible acid trip. I've watched people screw up and be unable to find their errors BECAUSE they were using it and thanks to the illegible colour contrasts of their favorite "gee ain't it neat" theme. I didn't like it when I first encountered it in Turbo Pascal 4 some thirty-odd years ago, and I've seen ZERO improvement in what it does or how it works since then. As cute as being able to see "hey you didn't close that string" is (what I rely on brace matching for) the simple fact is the rainbow-striping of the text makes the actual text range from painful to outright impossible to read! (seriously, the next joker that thinks blue on black text belongs in their editor is getting my 3 pound lump hammer introduced to their groin with great ferocity and passion!)
... and that's a good deal of why I like Flo's Notepad 2, it either lacks those 'features' or lets me turn them off.
More than anything I'd be a lot more forgiving in certain editors if they provided more options for turning annoyances OFF.
The relatively low memory footprint and fast load times garner it high marks as well. I don't need to waste 35 megabytes and 40 seconds on starting up A FREAKING TEXT EDITOR!!! (sorry sublime and Atom, but you inhale upon the proverbial equine of diminutive stature!)
I don't want or need compiler integration, I know how to use the command line. I don't want or need browser integration, that's why I keep all three native browser engines open along with two VM's so I can test ALL engines not just whatever outdated version is built into the editor.
Of course that it just uses the windows standard shortcuts (^X^C^V^G^H^F) instead of agonizingly vague/cryptic bullshit -- like say what vi/vim/emacs does, and just lets me TYPE THE HUFFING CODE instead of dicking around between command and entry mode (like emacs) helps too. I wanted to screw around with that nonsense I'd still be using wordstar commands like it was 1984. ^K this uncle-huffer!
So many "professional" editors are just filled with garbage tools, garbage methodologies, and stuff that "Just gets in the damned way" when ALL you should really need is a overglorified notepad replacement. There are just far too many times in other editors where I end up screaming at the display "Oh for F* SAKE JUST LET ME EDIT THE DAMNED CODE!!!"
It's hard to say what's worse -- the garbage 'modern' tools slopped in there that do nothing but get in the way, or the needlessly cryptic outdated trash like 'vi' where it's almost like these asshat clowns miss the days of Wordstar and Edlin. I wanted to waste time dicking around with pointlessly cryptic editor commands I'd drag out my Trash-80 model 12's Xenix so I can use 'ed'.
As with a great many things, I prefer the middle-ground atwixt the two.