The table below lists the 2010 regular season +EPA totals for each team by position. Although it doesn't consider free agent losses or injuries, this might be considered a good starting point for determining defensive draft needs.
Unfortunately, defensive positions are not so cut-and-dry. Depending on the base scheme, there are varying numbers of DEs, DTs, and LBs. (The 49ers don't even have a DE position.) Plus, players can sometimes be designated different positions from week to week. Advanced NFL Stats ultimately classifies players according to their most frequent designation in each game's official playbook.
So take these numbers with a heavier does of salt you otherwise would. In fact, it may be wiser to consider the DE and DT positions as one whole, at least for the 3-4 teams. Further, a team's scheme may use its linemen as space-eaters, allowing LBs to make plays, while some teams may expect their linemen to penetrate more often and make more plays.
The table lists each team's league-wide rank for each position. The top third is shaded in green and the bottom third is shaded in red. Defenses that ran a base 4-3 were a minority for the first time as of 2010. There were only 15. To make apples-to-apples comparisons easier, an asterisk leads the 4-3 team abbreviations, so sorting the Team column will group like base defenses together.
Compared with the table for offensive players, there aren't as many basket-cases. A sieve of an offensive line or a poor QB could ruin the entire offense, but perhaps individual defensive positions are not as inter-dependent on their performance. In other words, a good safety can make a big impact despite (or because?) of poor line play. Just a thought.