When should I choose a PDW as a primary weapon

You need to make sure you use the defibrillator on their torso. If it fails, try again, if it fails for a second time, try going prone.

Keep in mind there are certain times where it might bug out and treat your team mate's body like it's in another location, for example, when someone dies on stairs, and their body rolls to the bottom, every now and then, the game still acts like their body is where they died.

Here's information for the standard multi-player semi-auto rifles. There's also partial information for the M39 EMR, which you can only unlock through playing in co-op mode. I don't play co-op, so I'm unable to analyze that weapon.

I assume we're talking about these:

• MK11 MOD 0
• SVD
• SKS
• M39 EMR (Co-Op unlock)

Unlock progression

There's no significant difference between their unlocks. Their origin, Russian (SVD and SKS) vs. NATO (MK11 and M39), will affect which faction's holographic sight and red dot sight they get first, for example. But ignoring very minor differences, the unlock progressions are the same.

Damage

This earlier question points you to damage information for these weapons, from a weapon stat spreadsheet that includes other information as well.

Here's a table copied from that answer (thanks Jeff Atwood). For comparison, player health on a standard server is 100.

RANGE   5  10  15  20  25  35  40  50  60  80  100 meters
SVD    50  50  49  48  47  44  43  41  38  34   34
MK11   50  50  49  48  47  44  43  41  38  34   34
SKS    34  34  34  34  33  32  32  30  30  30   28
M39    50  50  49  48  47  44  43  41  38  34   34

So the SKS is lower than the others, but still decent on a per-shot basis.

Rate of Fire

Unfortunately the spreadsheet mentioned above says nothing about semi-auto rate of fire as of this writing. The problem is that semi-auto weapons don't have a rate of fire in the same sense that auto weapons do.

You'd think ROF is just "as fast as you can click, but with an upper limit enforced by the weapon." And while that's roughly true, it's not quite that simple.

Empty a few semi-auto magazines as fast as you can. You might expect to hear a regular rhythm constrained by the weapon's upper limit, but you'll actually hear something pretty irregular, including some very fast spurts. There almost seems to be a sweet spot, meaning it's less about how fast you click than about whether you click at just the right times.

Given that caveat, here's information on the MK11, SVD, and SKS. I don't co-op, so I haven't unlocked the M39. For a semi-realistic number rather than an optimal (impossible) one, I emptied 10 magazines for each weapon, timing with a stopwatch, and averaged the time needed... i.e., there's lots of room for observation error.

So a disclaimer: understand that these numbers are very, very squishy.

Pseudo rate of fire (rounds per minute)

MK11    210
SVD     215
SKS     240

Spread

I have no great idea for measuring this precisely.

What I did was to measure—on my screen with an actual ruler—the distance between the white reticule brackets when the weapon is equipped. Obviously the mm measurement will vary with screen size, but it'll give you a basis for comparison between weapons.

Note that this was not scoped in. Once you scope in, the reticule's brackets disappear, making it look like every weapon is equally accurate... which I doubt is true. My leap of faith is to assume that differences when firing from the hip will translate into differences when you actually aim. That could be wrong.

I've included a couple of other weapons for comparison.

Smaller number = better (tighter) spread.

Semi-Auto spread in mm

Weapon  Stand   Crouch  Prone
MK11    45      39      33
SVD     45      39      33
SKS     33      26      21

Other weapon spreads for comparison

Weapon  Stand   Crouch  Prone
AK-74M  33      26      20
M9      14      14      14
G17C    10      10      10

Overall

The SVD and MK11 are pretty comparable, as you'd expect since they're the starting weapons for the two factions. Personally I feel the SKS works well for front-line recon play. It's less powerful than the others per shot, but it has less spread and a slightly higher ROF.