I wouldn't say "the worst", maybe "the one you'll be most nervous about." Try not to worry too much. It is very hard to brick these.
And it sounds like your taking wise slow steps and doing your homework. You'll be fine, even if something does not go as you'd like.
Choose the ROM you wish to try, then leave it on while you get used to it to see if it's what you really want. Maybe there are features you consider must-have that are missing and are in another ROM. Maybe there are things you really can't stand (5x5 icons) that you want gone. Then look for another ROM that better suits.
Lastly, as I think you've seen, folks here are very very good at helping get us out of potential trouble. (I came from a Sprint Pre+ too, and have been helped every time I've needed it.)
Good luck!