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Paintable acrylic latex is solid, but I'd actually push back on the idea that you need to overthink the caulk choice itself. The real variable is whether you're dealing with interior or exterior, and what kind of movement that frame experiences. Interior door frames that aren't exposed to weather? Acrylic latex works fine. Exterior or anywhere with serious temperature swings? Polyurethane or paintable silicone will hold up better because they don't shrink as much.
On the backer rod thing - that's true for bigger gaps, but here's what people miss: if your gap is uneven (and door frames usually are), a backer rod won't sit flush. Instead, cram some rope caulk in there first to take up the irregular space, then go over it with your regular caulk. Rope caulk is basically a putty you push in by hand, sticks to nothing permanently, and lets you fill those weird spots without the regular caulk folding into the void and cracking later. Saves you from having to redo it in six months.
Keep your finger wet while smoothing, not dry. Dry finger drags caulk out; wet finger pushes it into the gap and seals it properly. Let it cure fully before painting - check the tube, but usually 24 hours minimum.
The gap size matters way more than brand - anything wider than a quarter-inch really needs backer rod first, otherwise the caulk will shrink and fail. For door frames i'd go with paintable acrylic latex if you're planning to paint over it, or silicone if you want something that lasts longer and handles movement better (doors shift seasonaly). Are you dealing with interior or exterior doors, and is the gap pretty uniform or does it vary a lot around the frame?
I've sealed plenty of door frames around the house, and the one thing that actually made a difference was doing the prep right - clean out any loose stuff, let it dry completely, and yeah, use that backer rod if the gap's decent-sized. For interior doors I stick with paintable acrylic latex since it's forgiving and takes paint well, but if you're doing an exterior door exposed to weather, silicone or polyurethane holds up way better even though it's messier to work with. The caulk itself matters less than making sure you're not bridging a huge void with it - that's how you end up with cracks down the road.
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