This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
I agree with Colin. There isn't an appreciable performance difference between the two tag libraries, but JSTL is a standard part of J2EE, and Struts tags are not. JSTL tags are also much more powerful than Struts tags. I generally use Struts tags only when there is no equivalent JSTL tag (<html:xxx> tags, for example).