Running vest vs frameless pack?

Will you be actually running, especially downhill? Are you doing overnighters or just day trips? If running, especially for one-day outings, then the Vest is the way to go. If hiking (not running), the vest has some advantages for day trips, but for overnight trips, a Fast Pack or a traditional pack like the Burn would probably meet your needs best.

Typically not running, used for 1-2 nights. I’m looking at the UD Fastpack 25-35 models.  I enjoy the freedom from hip belts but find the shoulder straps on traditional rucksacks apply too much pressure around the pectoral area when not using a hip belt.

It is a weight issue.
I really think that carrying my race gear in a GG Burn like backpack would be just as comfortable as having it stuffed in my running packs. Yet, with that gear I do prefer the running packs, but that is because a Burn would simply have way too much volume, making a regular backpack style bag annoying because such a backpack cannot be compressed enough to efficiently store the gear. Plus the running packs don’t bounce when running, which is a must.
When it comes to packing gear for a hiking trip then I’d definitely wouldn’t want to go without hip belts. In my experience bellow 5kg I don’t need hip belts.

Eins