This seems to be an unsettling time for Pandora Media (P). User growth has stalled, and now even its largest outside investor is calling for the streaming music pioneer to put itself up on the bidding block.

However, we can't assume that the grass is greener on the other side. Pandora's biggest rival -- Spotify -- is struggling to turn a profit, and that's the model that many of the tech giants including Apple (AAPL 1.38%) are championing. 

Spotify's parent company posted fresh financials yesterday, detailing its fiscal performance for 2015. It was another year of heady growth. Revenue soared 81% for all of last year, well ahead of Pandora's 26% increase. It's clear that Spotify is the speedster here, and the market generally celebrates its model that relies largely on premium subscriptions to generate revenue. Most of Pandora's users are freeloaders, taking advantage of the platform for free in exchange for putting up with a steady flow of ads.

Spotify offers a free platform with limited features and occasional ads, but 89% of its revenue last year was generated from subscriptions. The balance comes from advertising revenue that has more than doubled over the past year. Pandora is the other way around. Advertising revenue was good for $933 million, or 80% of last year's top-line results.

Lend me your ears

Logic would seem to dictate that subscription revenue is the way to go. It's proof that you're attracting an audience with disposable income, and you're not going to generate $9.99 a month from freeloaders based on ad consumption. Apple Music -- like Spotify -- charges $9.99 a month for its service. Apple's big tech peers that also have some skin in digital music have also gone the subscription route. What if they're betting on the wrong digital horse?

Spotify posted a widening loss in 2015. Pandora saw is adjusted profit cut in half, but at least it was still profitable on that basis. With artists, labels, and songwriters looking to get paid with escalating royalty rates, it isn't easy to turn a profit on streaming subscriptions. However, we did see ad revenue at Pandora and Spotify grow faster than subscription revenue, and there's more upside there as sponsors begin to pay up to reach the juicy demographics of the mobile earbud-donning set.

Advertising is a big deal at Pandora, growing even at a time when its user growth has slowed to a crawl. It may seem odd to say it, but could advertising be the better model than subscriptions at this point in streaming music's life cycle? 

Apple doesn't break down the financials of its digital music platforms, but the consumer tech behemoth as a whole is experiencing shrinking margins and profits these days. The other tech juggernauts that jumped into this market aren't making much of a dent, likely losing a lot of money in the push to gain relevance with the mobile masses. 

Pandora is in the right place. Its active listener base has only grown from 79.2 million a year ago to 79.4 million as of the end of March, but at least it's a massive audience that's hooked. Listener hours have grown slightly faster than active listeners over the past year. There's a lot of things that Pandora has done wrong over the years, but the one thing that the market seems to dismiss is that it may be the one with the more sustainable model for a profitable existence.