It really depends on your budget, and how serious you are going forward as a homebrewer. Basically, stainless steel brew kettles are a more expensive initial investment, but they are more durable than aluminum brew kettles and can be cleaned with a wider variety of cleaning solutions. Since you are a beginning homebrewer, you may not want to invest too much money into your equipment yet. In that case, a quality aluminum brew kettle will probably serve your purposes just fine (if you properly maintain your aluminum brew kettle, it will last you a long time).
