I'd been thinking about trying a straw, as DS gums away on the soft spouts, but doesn't really suck that much. On the harder spouts he sucks, but tends to have a harder time if he has to lean back and tilt the cup up.
Do the cups with straws have the straws going down to the bottom of the cup, or are they just a straw-shaped nubby, if you kwim?
Sounds as if the Playtex may be worth a go!