i have both, and i would highly suggest buying both. they are great games.
but, for a rental i would suggest red steel. you can get more into it in a short amount of time. zelda is amazing, but much more involved, with much slower advancement.
unless you just want to experience what everyone is talking about to be the best game on the market. then go for zelda, just so that you can see if for yourself.
but, all in all, i would say rent red steel, and buy zelda as your next game... if you like red steel, get it down the road.