best source for Pandora

Other's know a heck of a lot more than me about digital.

Isn't Pandora's signal quality the limiting factor? Do you pay for premium Pandora, and do you know what that signal's specs are?

I like Pandora for it's exposing me to artists 'like' someone I already know, more important than quality. Mine is generally further limited by computer on board audio chip, or home theater/smart tv quality.

I stick to free basic.I then go to LP or CD in music system.

Also, a lot of new discoveries are more enjoyable via YouTube Videos for me, I may never buy LP or CD, never thru music system. My darn good home theater sound system helps make those videos enjoyable.

Pandora's sound quality isn't that great.  I use it for background music, but that's about it.  Which I realize doesn't answer your question.  You could try Roku, Chromecast, or something like that, but I don't think it would improve sound quality.

So this is more of a hardware question.  I'm fine with the quality of Pandora.  It's just background music while working around the house or on the patio.

Just looking for info on the best device to get it to my preamp.

Bearing in mind it’s limitations due to streaming quality I do not think anything is going to make much of an improvement over your present iPhone or Kindle.

I admit to having streamed Pandora for years, well before Tidal and Qobuz existed in the USA.
It was always background music and a great tool for discovering new artists.
I used and still do my Samsung smart TV to stream it via it’s toslink output to my DAC.
For what it is, it sounds decent enough.

 Maybe the Audioengine B1 might be a solution.  Priced at $189 with a 3 year warranty and aluminum case to boot.   Uses a AKM4396 dac chip.  Has  RCA outputs to enable hook up to your preamp.  Also a toslink output if you would like to run it into an outboard dac.   Set mine up and paired it and never needed to touch it again   

Raspberry pi running Volumio.

FWIW. Subscribe to Pandora+ for $5/mo. primarily to get “better” sound quality.  
My experience with Win10 PC is that Pandora online resolves music much better than the W10 app, where I believe earlier research indicated that W10 app is def bandwidth restricted.  The PC also resolves better than Pandora app on Xfinity. If I recall, the iPhone/Pad thru the same system resolves the same as W10 online Pandora since now I only use Pandora on iPhone when mobile thru AirPods.   

I would say that some cuts coming thru the PC setup make me look up and take note to the pretty incredible sound quality coming thru a high quality consumer gear setup.  
Bottom line, test out the $5/mo. service being sure that the online app is set up as “best sound available” (or something like that.)

$0.02

Similar experience with Pandora.  Using  andriod phone thru a BT device the dac indicated 44.1k.  Using a chromebook the dac indicated 48k.  I have the premium tier and like the options it offers.