Thank you so much for helping me choose!
I personally had a Petite&Mars stroller, actually 2, at home to review - the Royal 2021 which is reviewed in depth HERE and the Street Plus review of which you'll find HERE (I used to work near the brand so had an opportunity to try those). The brand is on the affordable side, and the strollers are both on the larger mid size spectrum for that category, though they are VERY spacious in the first place, and the brand itself is ok, nice for the price, quality-wise.
There is definitely a difference, even in the later iterations - the Royal 2021 is sleeker, a bit thinner after folding, kind of more eôegant and less chunky. I also liked its larger hood more. The Street+ RWS has the same wheel quality as opposed to foam or inflatable wheels of the previous generation), though it's still a bit more robust, frame-wise, and the plus for the fashion-conscious moms are the interchangeable canopies and padding so you can easily swap the stroller's look.
Functionally, they are similar, now with similar wheels, though the Royal would be better for a mostly urban mom, while the Street+ RWS has a more sturdy frame and a bit larger/more accessible basket.
My own choice between the two would probably be Royal (also for the a bit longer seat), though again, if sturdier is what you need, the Street would be it.