I would go with dionysus. Gucci, to me, is generally a trendy brand. I consider most of their items to be seasonal or good for 1-2 years. Well-designed and understated bags are least likely to fall out of fashion.
Dionysus features the GG canvas, something that Gucci is known for and has been doing for years. I was given a vintage Gucci bag years ago from my aunt's collection. She babied it and so do I. The GG canvas looks good as new still. GG canvas has also been in high demand as of late, thanks to the resale market. To ride this trend, Gucci brought back some vintage styles with the GG canvas, those bags are actually some of my favorites. Hardware detailing on dionysus is also "small." While the hardware itself is large, it's not loud. Because it's not obviously prominent, the buckle recedes into the bag's overall composition/style.
A little blurb before going into marmont: Leather that has quilted detailing is a fad. Large hardware is also a fad. Chanel does have quilted leather but cross-hatched quilting is iconic to the brand, hence why it's a classic to Chanel. Think about it this way, ten years ago, were quilted leather bags being largely produced, other than Chanel handbags? In the late 1990s to early 2000s large hardware and/or a lot of hardware was also in fashion. Many bags featured lots of hardware. When the economy went down, having money and flaunting it wasn't good. The trend went towards less is more, so less hardware and extra frills, and less obvious/prominent labels on the item itself. With the economy improving in most recent years, we've seen a rise in louder designs. Having money and flaunting it isn't a sin right now. There is demand for "bigger or more," from the ultra rich and younger audience. Gucci has been catering to the younger audience as of late, hence some of their more trendy and at times, obnoxious, designs.
So, marmont is trendy because it's a quilted bag with large and prominent (in your face) hardware. That heart on the back is definitely a fad. I have no experience with Gucci leather but marmont looks like smooth calfskin leather to me... I stay away from smooth calfskin like the plague, no matter the brand. I find that it easily scratches and if kept in not so ideal conditions, can crack. I baby my bags, but not to the level that smooth calfskin requires. Dionysus is more "classy" because it's understated all over. It doesn't follow a specific trend. It's just a bag that is designed and composed, in an artistic sense, well.
But if I were you, I would just go with the bag that makes me happy and fits my lifestyle, regardless if it's trendy or not.
