Flatwounds for my bass

You should try a few different sets till you find something you like. Lots of people love Daddario chromes. They're on the brighter side of the flatwound spectrum. Labella flats are another great choice. They're more mellow and thumpy than chromes. More expensive but my preference for flats.
Here's a great place to buy strings:
http://www.bassstringsonline.com/Flatwound_c_255.html
The owner Jason is a TB member and will give you special pricing. Send a PM to SLaPiNFuNK and let him know you're going to order strings from him. Hell of a nice guy with an uncanny level of product knowledge.

Also, if you want to do some reading, here's lots of discussions on the topic:
https://www.google.com/search?as_q=...=any&safe=images&tbs=&as_filetype=&as_rights=

 

I recently changed from rounds to the Daddario Chromes and really like them.

 

The Fender 9050CL set switched me to flats a couple of years ago after being a rounds player for over 35 years up until then: balanced, consistent, both string-to-string and up the neck, can growl or mellow as need be, inexpensive, lasts forever. Even if you eventually go all the way to the thud of Chromes or LaBellas, the Fender are a good transition set from your steel rounds. You might even like them and stick with them, as I have.

 

+1 on the Fender 9050CL's. Also Sadowsky Black Label flats sound great on my P.

 

Im looking to switch to flats too. I play the stock rounds on my MII Sqiuer Jazz bass. I want a mellower sound with a bit more growl. My band plays heavy but melodic. I finger mostly but pull and slap some. I was wondering how much difference there is between 105s and 110s on the E.

 

I like D'Addario Chrome Flat mediums.

 

La Bella 760FL if you want "the" flat sound.

The Fender 9050CL set is also fine, and more versatile.

The long scale Pyramid flats are great, too, if you want thump and a luxurious feel.

 

Not to denigrate the well-meaning folks who have chimed in so far, but there is no way we can give you an adequate answer without at least some information as to the tone you are going for and/or the style of music you would like to play.

 

My experience with flats has been:

Rotosound- The brightest by far but they can sound a bit thin and lack mids. They are very stiff also so a set of .40s will feel like a set of .45 rounds IMO.

D'addario Chromes- A nice middle ground but IMO they lack character sort of like a generic flat wound sound. Tension felt pretty moderate to me.

Fender Flatwounds- Lots of mids and more dead sounding than the others mentioned (not as much zing) and they are my personal favorites so far but the 5 strings sets have a weird tapered B string. Also pretty low tension for flats.

I have yet to try any others but this is what i've found so far. Also this video helped me with deciding on a set of flats when i first started using them: https://www.youtube.com/watch?v=6R2LOXMqyg8

 

Yes, I too had a set of Rotosound flats on a jazz bass. Tone wise they sounded similar to bright nickel rounds, not the dead flat sound I hear in most flats. The feel of the strings threw me off too, as they sound so much like rounds.
I definitely would not recommend the Rotosound Monel flats, there are flats with truer tone on the market which cost much less.

 

I have GHS Precision Flats on my Precision. I like them because they are 'dark' sounding. They have a very strong purcussive attack that I like. They are very focused on the fundamental tone with subdued over and undertones. Once played in they hold tune extremely well.

On the negative side they start out very unbalanced and it does take some playing time, but they do become better balanced as they break in. String tension is high, and necessitated a completely new set up to include a truss rod adjustment.

 

I have GHS Precision Flats, too. +1 on everything Linnin said. I love their tone and percussive quality, and it's hard to overstate how well they stay in tune.

 

I'm a huge fan of nickel flats. Therefore, Pyramid flats are on all but the P bass, which has Chromes (one gui**** prefers RWs - Chromes sound closer to RWs than flats to my ear). Silky feel, medium tension, great tone, last forever...

When my 4001v63 is ready, I'm going to try a set of Optima nickel chrome flats... I've heard good things about them...