These are my personal top 3 LED taillights that I have used a lot and can make informed comment.

1. Cateye LD1000 20-30USD - used 1 year
pros - pretty bright; unique side leds; AAs last longer
cons - heavy from 2AAs; extra width causes thigh rub/interference if using setback seatpost; spontaneous shutoff from battery contact design
comment - i like it but it hits my legs due to width and setback seatpost i use (don't have this problem on other taillights).


2. Performance Flashpoint 10-15USD - used 4-5 years
pros - leds are among brightest in 5mm size, 9 of these leds makes this a bright taillight; wide beam angle improves visibility; also serves as reflector; Performance takes these back when they eventually fail
cons - AAAs need to be recharged more often than AAs; poor battery contacts result in spontaneous shutoff, battery short circuit, complete failure; button contact can fail too
comment - cheap on sale, really bright, dang things fall apart in ~15 battery changes - i buy several so i can send bads ones back for replacements from Perf - shipping makes this merry-go-round system cost prohibitive, would work better if you live near a retail Perf store

3. Planet Bike Super Flash 15-20USD - used 0.2 year
pros - 0.5W led very bright; compact size makes easy to fit; battery contacts/holder seem to be best design of the 3 taillights described in this post
cons - none so far
comment - haven't used the PB SF much but it's so bright it deserves to be on my top 3 list; PB includes mounts for seatstay mounting, nice touch

My amber xenon strobe is the brightest taillight I own, however my 12V lighting system (power source) is broken now so using LEDs again.