It's complicated for a number of reasons, but here's some things I learned from fiddling in Excel.
For starters, Dodge will mitigate 100% of any hits you dodge, but you'll only Dodge D% of the time.
Armor will mitigate A% of every hit, but that value is dependent on the level of the enemies attacking you (see this question).
So the basic question is "what has to be true for D to be greater than A?"
At level 60, my calculations show that 520 Armor will give you just over 15% damage reduction from armor. So you only need 520 Dexterity for Sieze the Initiative to start being better.
However, this is only true if you have 0 base Armor and 0 base Dodge, which is probably not true! If you have 100 Armor you only need 420 Dexterity - unless you have 5% base Dodge, in which case you'll need 700 Dexterity on top of your 100 Armor...
You can use this table to estimate how much mitigation you'll get from armor when fighting level 60 monsters:
If you look up your base Armor + Dexterity here and compare to your base Dodge + 15% you should be able to tell which is better in a given situation.
Overall it SEEMS like it's pretty easy to stack Dexterity and have Sieze The Initiative outperform The Guardian's Path, but I tend to stack Dex anyway and definitely have not attempted to stack Dodge, so I'm not sure which is more viable in the long run.