Since the part has a ball joint in it, buying new is more advised, though few people ever replace the parts down the road the ball joints do wear out, why put an old one back on when a new one is really not that much more expensive? Now if it was an upper arm where it's like $400 new, I'd definitely go used, but an extra $40-50 is worth it for the peace of mind.
Also if you really just want to save money, you can likely find it even cheaper used if you call a few salvage yards, if it's $100 new you can find it for $25-30 if you make the effort.
If it was me though, I'd replace both sides with brand new. In fact I wonder if if they're that cheap for the UCF10, usually anything link related is minimum $200 on these cars.