Just went through the decade numbers using basic scoring, 4 pts for TD. Pretty interesting look. It becomes clear at the end there is only 2 choices as RC pointed out, Manning or LT.
The interesting thing is that there were 2 players that led the league in fantasy points scored twice in the decade, and neither was Manning or LT. Marshall Faulk started the decade out with a bang leading the league in both 00 & 01. Holmes took the torch from him for the next two years leading the league in 02 & 03. Faulk's problem is he was on the back 9 of his career and after 01 did very little. Holmes had a great run from 01 - 03, but fell off after that.
The guy who has not been mentioned that likely deserves a top 5, if not a top 3 mention right behind Manning and LT is Alexander. His run was longer than some of the other top performers at RB. From 01-05', he never finished lower than 11th and led the league in 05'. He also notched a top 3 in 04; and two 8th.
Brees is another one that quietly should be considered in that next tier. His issue is he got started a little late, but since 04 has put on a good run. 04 & 05 were decent at 16th & 17, but in 06 his fun started. He notched top 10's in 06 & 07 and took home a #1 last year (something Manning never did) and finished 2nd this year, just missing that 2nd #1 for the decade.
Now for the top 2. What separates Manning and LT for the pack? CONSISTENCY! Manning was easily the most consistent of the decade. He was Mr. Reliable and could always be counted on top finish in the top 10, something he did in a remarkable 10 of 10 years this decade!! He never led the league, but did finish 2nd in his record breaking 04 season to Culpepper. Manning also had 2 other top 5 seasons in the decade.
As for LT, he wasn't quite as consistent as Manning, but for a RB, his consistency was amazing! From 02' to 07' LT never finished lower than 6th in overall scoring. He only led the league one year in 06, but what a year it was! That season LT racked up a decade high 427 fantasy points! He also racked up 4 more top 3 finishes giving him a total of 5 top 3 finishes in a 6 year span. That is more than just consistency, that is dominance like we did not see from any other this decade.
In the end, manning was money, but LT was dominant! I will take LT's 6 year reign of terror and dominance over Manning's 10 years of consistency with out the high end results than dominate leagues.
My Fantasy Player of the Decade is LaDainian Tomlinson.