Something that is suitable to your level. If you aren't a professional, don't invest in the most expensive, gold-infused rosin. Likewise, as a professional, don't cut corners with a cheaper block of rosin meant for music students. Good rosin is high quality. There are lots of "cheaper" rosins out there that market themselves as competitive because they include a cloth or a carrying case, but extra accessories will not compensate for poor quality. I assure you; I've tried to travel that road to "savings" many times, and no matter what, I have always found that if something comes in a kit, the quality of each piece of that kit is much lower than if you purchase piecemeal. Now, sometimes that is ok, sometimes that is what you want as a beginner or when you are buying a simple first aid kit for your car, but it won't work for intermediate or advanced cellists.