Tough one ... I think most would say Hawkeye... but it really depends on what you need utility wise.
Hawkeye: consistent power drain on SP1 and bleed (great for many AW fights)
Elektra: can shut down magik limbo, electro return dmg, and other various champ abilities impacted by the reduction of ability accuracy... when played right by placing either stun debuff, or bleed or if bleed immune, armor break debuff
Edit: just noticed that you said which to 3/45 (had incorrectly assumed 4/55) -- I'd r3 both of em
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Hawkeye: consistent power drain on SP1 and bleed (great for many AW fights)
Elektra: can shut down magik limbo, electro return dmg, and other various champ abilities impacted by the reduction of ability accuracy... when played right by placing either stun debuff, or bleed or if bleed immune, armor break debuff
Edit: just noticed that you said which to 3/45 (had incorrectly assumed 4/55) -- I'd r3 both of em