Here's the breakdown
CM7: if you want the
core Cyanogen Gingerbread experience. This is where Isaac gets some of his stuff for MIUI. Great if you want a stable experience, with tons of modding options. CM7 is open source, making it easier to fit to the Triumph natively. CM7 has a wider user base than most other ROMs (widest user base, possibly) and a more active community.
MIUI: if you want a really cool-looking phone. It should be noted MIUI is the
king of visual enhancements and theming; you can hand-pick individual elements of thousands of themes, and create the perfect mix-and-match theme of your own that way. MIUI also has the smoothest, best-looking graphical animations. If I remember correctly, MIUI is a
port, which can leave rooms for bugs, as the OS is not open-source. It was going to be, but there are some doubts about that now. MIUI is based of Gingerbread.
It should be noted that the developers of the above ROMs, Isaac and Tickerguy, are awesome. Also, there is a lack of overclocking support for the above ROMs.
If you want overclocking support, I recommend you use bROM. Use bKernel on Froyo-based ROMs as it has better overclocking features than UmphKernel (up to 2+ GHz).
bROM and Princerly are both Froyo-based ROMs. I, personally, do not know any reason to stick with Froyo (you'll be 2 OS's behind soon)
but if you have a compelling reason to use Froyo, use bROM.
EVERY TIME you modify something important (eg. change ROM), make a NANDROID backup. No exceptions.
Because the one time you don't, your phone will fail and/or get bricked. <--- Spoken from experience with 3 Android releases. I swear there is some evil devil manipulating when the phone will fail.
Hope this helped.
I was asking about which ROM is better, not only for me, but in hopes the discussion would benefit others as well. If somebody acts childish, well, that's them. What if I told you I was 15? 35? 20? 
Does it matter? Although, I think Brandon already said he was 14. (look at his name, b_randon14)
