Unnatural Assumptions It would be natural to assume that the main way Defenders score points is with clean sheets, and that you should pick your defence on the ability of that player's team to keep clean sheets, after all that is a defenders job isn't it? This may be the logical thing to assume but there is a lot more at play than just clean sheets.
The top scoring defender in the 2010/2011 game was Leighton Baines of Everton with 178 points.
But if you look at how those points were broken down it tells a story you may not expect.
Everton kept just 9 clean sheets in 38 games, only half of the league high of 18 achieved by Man City, where the Manchester City Captain, Kompany, who played in an almost identical number of games to Baines scored only 95 points, Baines got 178 even though his side kept only half the number of clean sheets.
Baines' 178 Points: Clean Sheets: 34 Appearances: 70 Goals: 25 Assists: 33 Bonus: 20 Goals conceded deduction: -4 From this you can see that that just 19% of Baines' points were scored through achieving clean sheets, in fact a majority was derived from the fact that he appeared in every game Everton played during the season and was a key player for them achieving 20 bonus points and being one of the league's highest assisters.
In fact for around £8m Baines achieved more points than the league's top scoring striker Berbatov who would have cost you around £9.
2m.
You should apply a few strict rules when picking your defence and they should be prioritized in this order:

1. Will he play in the first team almost every week
2. Will he get goals or assists or both
3. Will his team keep at least an average number of clean sheets (8 or more)
4. Is he one of the top 3 key players in his teams' starting 11

On this basis, the best choice for defenders is almost always full backs, they attack with far greater frequency and are therefore much more likely to get goals, assists and bonus points which can make a huge difference between a high scoring defender and a low scoring one.
Goal scoring Center Backs (the tallest that have a rack record of chipping in with 4+ goals a season) also come in to the same category, so players like Jamie Carragher and Rio Fredinand should be avoided.
Value is King The most critical driving factor for picking any player is value (not to be confused with price as high priced players can provide poor value and low priced players very high value), because you won't simply be able to pick the best, most expensive players in the league the most effective way to pick a winning team is to find the players that cost little but will score relatively high numbers of points, and there are plenty of them in the league.
They carry more risk but finding them is usually the difference between doing well or badly and a yard stick for this is "pints score per million pound of spend".
Now Kompany would have gotten you approximately 16 points for every million you spent on him, whilst Baines on the same hand would have got 23, make no mistake, this is a huge gap when it comes to value.
Now if you compare this to any striker, then pound for pound Baines would have been one of the best value players in the game and a must for your team even though he is one of the most expensive defenders in the game, but he is an exception in the league because he meets all the criteria set above in some abundance, he is the exact model of what you should be looking for in a fantasy football league defender.
Lets take a look at the points per million value of some selected defenders in the league and their clean sheets: Kompany - 16 Points/Million - 18 Clean Sheets (Man City) Vidic - 20 Points/Million - 15 Clean Sheets (Man United Baines - 22 Points/Million - 9 Clean Sheets (Everton) Hangeland - 24 Points/Million - 13 Clean Sheets (Fulham) Shawcross - 20 Points/Million - 9 Clean Sheets (Stoke) El Mohammady - 24 Points/Million - 9 Clean Sheets (Sunderland) Whilst the list of highest scoring defenders are full of players who are firm start 11 members in the big 4 squads it's important to remember this isn't always as significantly determined by the number clean sheets they keep and doesn't always provide the best value, there are a lot of other factors that divide those that are worth having and those that are not, and the best value will often be found by spotting those that:

1. Have a solid starting 11 place and are a key member of their team
2. Will score 3+ goals or get 5+ assists
3. Will get an average number of clean sheets or better (8+)

Top Tip When it comes to value it's far better to select a player who will keep an average number of clean sheets but who is a key player for an un-fancied, mid-table side every week and contributes with goals or assists, rather than to pick one who will just keep a big number of clean sheets because plays for a top team.