Go for one with the best (lowest temps), usually something with 3 (some 2) fans.
temps that affect boost limiter kick in at 54*C, so more of a "problem" with air cooled cards),
hence getting the one with the lowest temps under full load, will maximize your boost clocks.
with brands like palit/zotac/gigabyte (windforce) i wouldn't go with their cheaper stuff, they are good value,
but there is a reason why the coolest (and fastest) cards are usually from asus/msi (or the top model from GB),
which have beefier heats sinks.
lower grade coolers are most of the time using smaller and/or less heat pipes (sometimes not even copper), the fins have a matte finish,
when heat sinks on "better" cards (performance) are more of a glossy/shiny metal, and are much higher density.
chips for the top cards are usually heavily binned, so you should also see a bit more oc potential just on the chip itself.
power/vrm etc is most of the time also not an issue on those cards.
on 900/1000 series i saw the highest sustained clocks on the msi gaming cards, switched to water after that,
so no personal experience on the RTX 2xxx air cooled cards.
if you can, check amazon warehouse/microcenter for open box/used cards,
they offer 15/30 day return, and i got some nice cards one and even two models higher than budget would have allowed if getting a new card.
(my water cooled 2080 was open box from amazon, for less than what any air cooled card i was interested in would cost new).
either way, use afterburner to max out sliders for temp/power limits (not voltage),
increase vram clocks until you hit unstable clock, back down 50 MHz,
then use the oc-scanner to scan for oc, apply the curve, which is most of the time very close to max clock the chip can reach,
but is helps using less voltage for anything below max boost clock).
if you go with GB, make sure you get a rev1.0, as all the cards i got being rev1.1 (higher) were coming with lower grade vram and even performed less for avg oc.
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