Joey -
I like the Boomers too. Given my druthers, I find that Rotosound Swing Bass strings are just perfect for me in the 4 string set, but somehow, the Rotosound low B is totally not happening! I really like the piano-like zing of a new set of roundwounds for the 3 days or so that it lasts. But most of the time, I'm not all the keen on really bright strings. Rotos are stainless steel wrapped, but generally I would prefer the tone of nickel plated strings. Stainless maintains their sound much longer, but if you don't like the sound of the strings, why would I want it to keep sounding like that?!? :-) Rotos are stainless, but don't sound like that to me.
I still vary 5-string sets with different basses, but I favor the Boomer 5-string sets if the particulars of the bass don't favor something else.
When I had my last Series II built, I had the factory set it up with Markley Blue Steels which seemed kind of interesting at the time (this was a long time ago, in the early 90s and these strings were new). This string has a very nice quality feel, but just sounds terrible to me. That bass has had Boomers since then, although I will go for long, long periods of time between changes.
On some of my other 5-string basses, I found that I liked D'Addario Slowounds, which are no longer made. D'Addario says that advances in their manufacturing mean there's no difference between the Slowounds and the XLs. It sure doesn't sound that way to me - I find that the XLs have a pretty wimpy sound compared to the Slos, although I think the low B does vibrate better in the XL set. I've got DR Low-Riders on some Modulus basses as well, although they seem a little thin to me too compared to the Rotosound 4-string set.
On guitars, I used to use D'Addario XLs most of the time, but over the last 10 years, many manufacturers have brought out pure nickel wrapped roundwounds, like they were in the 60s (not that I was playing then). The Gibson Vintages or even the Ernie Ball Classic Rock 'n' Roll Slinkys are a huge plus for guitar tone in my book.