Saved me some time that.
Basically, Guidetti has the potential to become a terrific player, his attitude is spot on and from what I've seen of him (youth level and his loan spell at Brommapojkarna), he looks very good.
Elmander had a good run of games earlier this season, but hasn't really set Reebok alight since signing, has he? Wikipedia says 18 goals in 90 games, hardly prolific, especially not when you consider that he's been there in the prime of his career. He's about to turn 30, and would probably cost at least three times the wages Guidetti would. No brainer, really.