there is no re-locking. once you unlock there is no going back warranty voided. as far as what's the best rom, its way too early to say. you have to try them out yourself to form opinion on it. I will say that Virtuous Rom n Icylicious Rom has been getting great feedback.
Agreed there isnt to much development on the prime as of yet, but hoping it will come. As of now those two roms are mostly stock with a few visual mods at this point. Im really not up to try the CM9 as I have that on my phones, I like to have my tablet a bit different. I would love to see a rom like Roach2010 or Jcarrz1, even Mike1986 has put together on the original tf101, really enjoyed those alot.!!!
I think the ROM's are just basically a lil tweaked right now and more visual customization. Once the kernel is basically truly optimized, then we will have some bad-azz ROM's. At that point I will start the whole flashing of ROM's. I am holding out for a few more weeks to unlock my bootloader.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?