100% pens for me!!
I've used both types.
My pen pros:
1: Pens are MUCH MUCH less painful to the rabbit than clamps are, IF used correctly. Not saying a ham-fisted person couldn't mess that up, but in general, if you have a light touch and know what you're doing, the buns come away thinking you just had a bonding session with a little over-enthusiastic grooming. I've had buns crawl up on me and lick my face immediately after a tattoo. Rabbit ears are super thin, and require hardly any pressure at all to leave good clean lines that stay. MUCH less depth of penetration than most human skin. I don't even burrito the kits anymore when tattooing. The small flinches I occasionally see just tell me when I've been a little too heavy handed and need to ease up.
2: Cleaner lines. Bad handwriting can mess this up too, of course, but in general, pens leave much cleaner and easier to read letters and numbers than the dot letter/number clamps I've personally seen and used.
3: You can use a pen to do a small touch up on a fading or old tattoo at any time with little discomfort to the rabbit.
3: Pens are lightweight and easy for this little lady to use.
The downside would be:
1: replacing needles and batteries.
Now for clamps, I do have a few pros.
1: Sometimes people with a hard time regulating the pressure they use, a limited range of motion, or shaking hands (among other reasons) can prefer a clamp.
2: Also people in big commercial rabbitrys sometimes prefer clamps because it's a one and done, next bunny, type scenario, instead of the focus and individual attention required to pen out each tattoo. If you have to get through dozens or hundred of animals, clamps can be easier.
As for brands, I can't remember the clamps because I was just helping others with the process.
For pens, I only have my cheapo kbtatts modified-electric-tooth-brush pen. :lol: It works well enough, so I've never upgraded. I actually have professional tattoo equipment for humans, but using that would be more than a little overkill for bunny ears.