Hands down, the best,
CHEAPEST ear tags available come from hasco...
http://www.hascotag.com/
They have a booth at Louisville, that we raid every year. Last year, I picked up about 20 free blank cow sized, 10 black calf sized, and about 15 blank sheep sized ones for FREE. They also have a discount rack of seconds (both numbered and blank), which most of the time are a little off color- or have numbers imprinted on the buttons- for about half cost. Super great people to work with, and try to do anything to get us cheaper eartags. I think it's a family owned business.
This year, while down there- we picked up 100 cow (40) and sheep (60) tags, for a grand total of $30- tax free- show discount- and no shipping. We also pre-ordered 50 tags, and got the same discounted rates on them by picking them up at the show.
In terms of retention- SUPER in the cattle-- Don't think I've ever had more than 2 or 3 fall out. Really my only complaint with them is using the extra large, cattle tags on my sheep-- and the tags are simply too heavy and get ripped out.. Course, that's not the tag's fault.. It's mine for choosing to use them.. Risk I'm forced to take... but with my 4 tag; tagging system (plus ear tattoo), what's one more tag? And with my bad eyes, as big as the tags can be- is a plus... I really like their blank tags- use a marker and get plenty of black ink on there (double dose on each number)- and you'll never not be able to read it.. unless the Ytex tags which fade after about 5 years. To tell the truth, I've only used a few of their prenumbered tags, and after 10 years I think you'll still be able to read them, unlike some brands.
Now, the other complaint that some people have- is that the buttons are not self piercing-- which to me I prefer; as I'm often tired of having older buttons which get weak, and the pin pushes it to the side, and so you don't actually pierce the ear, but just bloody it up... I prefer these over any other kind of button... The only extra cost, would be a sharp pin to purchase and put on any Ytex, or Allflex tagger that you have.
Highly recommend them.
In regards to other tags, we've used Ztags, Allflex, YTex, you name, it we've tried it. After several years, it seems that we have a complete makeover with the cowherd's tags... I did like the Ztags- but my applicator pin rusted like an SOB; and so it didn't work right, Can't complain about them though... Even though I feel as if they tag working around made a slightly larger than normal hole in the ear.
Att his stage of the game, we're going 100% Hasco until they change something on us, and it becomes more expensive to use them... The crazy low cost is something that using an extra one here or there can be tollerated... Even though it's not happend.