There is no "comprehension" subtest on the DAS-II. The verbal subtests are most similar to WISC-IV Vocabulary and Similarities.
Overall, speaking as a user of WISC-IV (and other Wechslers), DAS-II, WJ-III-Cognitive, K-ABC-II, and SB-5, I would say that the DAS-II does the best job of separating various factors (e.g, not conflating visual processing with fluid reasoning and processing speed), and in allowing a tester discretion to choose an item set that is not tortuously easy for a gifted kid (one of my big complaints about Wechslers), with some nice options for out-of-level testing (giving a young child subtests that are designed for older kids and still being able to generate a normed score). It also provides a general cognitive ability score that doesn't load on Working Memory and Processing Speed, so the general score is more properly compared to a WISC GAI. I find that I can generally interpret the information I get on it without needing to do supplementary testing. It's become my go-to IQ test for most purposes, both the "how smart is this kid and what should we tell the school?" kinds of questions and the "why on earth is this kid acting out the way he is and what can we do about it?" kinds of questions.
However, I would not put much stock in IQ testing done at age 3. You're really testing how well the kid can cooperate with the tester, and kids that age vary widely, minute to minute, in terms of how well they can cooperate. Very likely that if you come back and test a few years later, you'll see some differences. I personally don't like testing kids younger than 5 (I've tested a few 4yo once the parents were really well-informed of the limits of reliability and my opinion that most of the time, we don't need to test young kids at all). If the kid was referred for behavioral problems, then fine, you test (within whatever you can manage to do given the behavioral problems!), but you also do other diagnostics to understand the behavior problems better.
Most diagnostic evaluations start with an IQ test, regardless of the reason for referral. It's not about the IQ per se, but about getting a nice broad sample of behavior.
The PPVT-IV is not an IQ test. It is a receptive one-word picture vocabulary test. I say a word, and you have four pictures to look at. You point at the picture that matches the word. I could look in the manual to get more info, but my guess standing on one foot is that it would correlate most highly with Wechsler-test Vocabulary or Information. Those are expressive language, though, and sometimes kids will do a lot better in the recognition format of the PPVT-IV.
