if you want to spend the money for the seasonic, get this one. 15 dollars more and you get 50 more watts, good efficiency, and it's modular (which is awesome). if you want a cheaper one, this is great too - it doesn't list it but it's >75% efficiency, which is great for the price. it's also in stock on newegg.
both of the ones you picked are good, but the antec is better (modular and has fewer rails with 7 more amps on each than the seasonic, which is great). it's better than the mushkin, so if you can get it for a deal, do it. you pay for the name at seasonic...they make good stuff, but it still costs more.