Depending on the type of campaigns (google, search partner network and/or content network) you're running and the traffic volume, here are some really insightful ones to dig through on a weekly basis. I've separated them by use, but there is obvious overlap where "Trending" reports can also serve to identify optimization opportunities.
TRENDING - Account Performance - Campaign Performance - Ad Group Performance
OPTIMIZATION & TWEAKING - Search Query Performance (Identify missing keywords that perform well and negative keywords to add) - Placement Performance (Identify strong performing sites on the content network to isolate on their own and eliminate poor performing ones from campaign) - Geographic Performance (Identify stronger performing areas to single out and target on their own for better cost control, bid management and to gain a competitive edge in certain high performing regions while reducing/eliminating exposure on low performing regions) - Keyword Performance (Identify top performers to go more agressive on as well as poor performing ones to eliminate or reduce exposure. Might also provide insights for negative keywords where impressions are high and CTR is low - especially on broad matched keywords)
While the other reports such as URL and Ad performance are very useful, you can manipulate, compare and interpret the data faster and more easily using the Adwords Editor instead on sifting through the info on excel.
I should also mention that depending on the search and traffic volume, you might also have to look at longer periods of time just to make sure you don't jump the gun and base decisions on too little data.
So it might help to also schedule or cross check the weekly reports with the same reports having 1 or even 3 or more months worth of data to make sure the data is statistically reliable.