I definitely would not under any circumstance trade Al Jefferson for Kevin Martin. Jefferson is a great fantasy option, he's had a slow start but he's rounding into form.
I'd consider trading JR Smith for him though...kind of feels like a coin flip between the two. Both will never be the top scoring options on their respective teams but at least Martin has shown he can be a scorer. He's still getting 30 minutes a game. His shooting %s are better than he typically is...especially with regards to his 3 point shooting. But I'm not really a fan of JR Smith's opportunity either.
Keep in mind that I'm a first year basketball guy too so take my opinion with a grain of salt. I've been really digging deep into info lately though haha.