Best is not subjective. Thomastik Infeld Jazz Flats are best.
 
Some people don't want the best, and that's understandable, but TIs are the best.
 
(If unclear, this is humor; my opinions tend to also be verifiable facts.)

Historically a fact ; Pyramid Gold Flats were a flat wound popular for Alembic bass's . They were often installed by Alembic at first sale.  I have a few sets in my string stash and a Series II strung with them .  
Elvis also thought that peanut butter and banana sandwiches were the best     ... ... BUT I do not concur .  
 
               For round wound strings I like Dean Markley Blue Steel XL 40-95 #2670.  At that gauge they work well in Medium Scale or long scale and sound awesome for Bass chords/ double & triple stops & quadruple stops... etc ...

Wolf - I think that Elvis's peanut butter & banana sandwiches were also pan fried in butter! Hey, that might work with strings if you want to try the Jaco route of smearing the strings with chicken grease...
 
On a serious note, string gauge is not necessarily equatable with tension. So flats can go the whole range from extremely low tension (TI Jazz Flats) to high (D'Addario Chromes) to extremely high (LaBella Original 1954, formerly the James Jamerson set). Never tried Pyramid Golds, so not sure where they fit in the scheme of things. Black nylon wrapped can have extremely heavy gauges but be very low tension.
 
And of course, most string manufacturers don't publish tension so it's trial and error!

Hello Harry,
                    If I recall correctly in one of our string threads such as this one (there have been a few here ) someone provided a link  to a tension  chart for various string manufacturers. That information might be somewhere on this site perhaps.    I think that string tension is often NOT disclosed so that one goes the route as you mention trial &error and then make multiple purchases to find your ideal preference.

For quite a while now I've only been using Thomastik-Infeld Jazz Rounds.  They sound great, they last a long time, and they are able to do what my fingers are trying to accomplish.  But then what I'm trying to do on bass is a bit outside the norm.

good old rotosounds swingbass sets does it 4 me..

I would say if you don't know exactly what you're after, the Alembic strings  are a great starting point.
 
If you want the super-bright piano-like tone, Rotosound Swing basses are excellent. (Although I moved from Rotosounds to the Alembic Strings)
 
Mica suggested I try some flats on my Series I the last time we spoke. I recently put D'Addario chromes on there, and quite enjoyed the change. These are not muddy at all, just a slightly more noticeable fundamental.  
 
An excellent choice for certain genres (chromes + series I + pick) = quite good for GD-style covers and such.

Good idea, i have fender flats on my precision. Gaves a thick sound, and 70ties style slapping sound...