I have a 2008 Mariposia Plus with the old carbon fiber stays and a 2010 Swift with the attached hipbelt and no stay option.
My Mariposia Plus is 21.1oz with stays and hipbelt (L torso M belt)
My Swift is 16.7oz with a little trimming of staps (nothing major)
I am comparing a frameless pack with a framed pack where both are avalible with a frame today.
Here are my opinions
I like the Dyneema grid on the Swift better than the 70D Nylon on the Mariposia Plus. It isn’t a big deal since I think they are both durable enough, but the Dyneema is definitely bomber.
Though the pocket configuration is very similar, the Mariposia Plus has the best pockets. The water bottle pocket is three dimensional (has a true flat bottom) which makes it very easy to use. You can fit two Gatoraide bottles in it easily. The Mariposia Plus also has a pocket above the water bottle pocket called a sundries pocket, which is great for things like aquimira, snack, headlamp or other items that might get lost in the pack.
The water bottle pocket on the Swift is smaller, good for one Gatoraide bottle (which is all I use anyways) and is low so it is easy to get in and out even without the flat bottom of the Mariposia Plus.
The Swift has a zippered security pocket inside for keys and whatnot. I find that a nice touch. The Mariposia Plus has no interior pockets.
The Mariposia Plus has a standard cord lock top, while the Swift has a dry bag type top. I am not sure which I like better, I guess that of the Swift by a small margin.
The shoulder straps of the Mariposia Plus are wide, much wider than any other pack I have seen. They are well padded and distribute weight very well, but they tend to rub some peoples neck. They don’t bother me, but if they did that would make it an easy decision. The shoulder straps on the Swift are thinner, narrower and more of an S shape. They don’t carry weight quite as well due to the thinner padding, but still do a fine job. They fit me well enough where I find a sternum strap is unnecessary so I took mine off.
The hipbelts are very different. The Swift ’10 has an unpadded very wide hipbelt, that I was skeptical of at first, but it is very comfortable and carries great with lighter loads. One thing to note is that I have a relatively slim 32” waist, but I couldn’t get any smaller and still be able to snug up the one size fits all hipbelt. The Swift also has great hipbelt pockets that have become such a handy thing to have. They are easy to work with one hand, though I wonder about the long term durability of the zippers. The Mariposia plus has a nicely padded hipbelt. It probably does better at heavy loads and is available in several sizes, which can be a blessing and a curse as I prefer a fixed simple sewn own hipbelt. There are no hipbelt pockets on the Mariposia Plus and the aftermarket ones leave a little to be desired in my opinion. They are well built and feel very sturdy, but require two hands in many cases to open.
Size: The Swift is bigger despite their similar size listings.
I have gone to the Swift for most of my hikes as I like to roll my Ridgerest up and use it as a frame and the Swift weighs less. For heavier, more difficult loads like a bear canister and five days worth of food like I will have on a JMT section hike this summer, I will go to the Mariposia Plus however.