What is the best time of year to see Constellation Crater?
Crater is at a Right Ascention of about 11h, meaning it's probably best visible in Northern Hemisphere spring. However, it's a faint constellation, and arguably there never is a "good" time to see it: none of its stars are above third magnitude.
Sirius is a single star, in the constellation Canis Major, just east of Orion. It's visible at some time of night during roughly 9 months of the year. The best time of year to see it depends entirely on what time of night you like to go outside and look. If you're like most people, and do your gazing between dinnner and bed-time, then Winter and early Spring are the best seasons.