I've only recently been experimenting with different UB builds lately, so forgive me if all this has been posted before. While this analysis of favor items doesn't apply only to UB, he was the inspiration for it. I was curious about the relative value of Mard's Hammer and Furious Blade, two assassin favor items that increase damage output in different ways.
Mard's Hammer: +40 weapon damage, +5% attack speed
Furious Blade: +100 health, +5% attack speed, 15% chance on hit to increase attack speed +30% for 5 sec
I've been using the calculator at http://www.demigoddb.com for some of what follows, but you can hand-calculate it yourself as well.
Let's take a UB at level 1, no other items, no abilities.
Damage/sec = 121/sec (168 average damage per hit * .72 attack rate)
With Mard's Hammer: 157/sec
With Blade: 127/sec, unless triggered (15% chance per hit), in which case it increases to 163/sec for 5 sec
For sake of an example, let's assume that UB is in melee for a 10 second period. At level 1, he would get 7.2 attacks in that period of time.
With the Hammer, he'd do: 1570 damage.
With Blade, let's assume that the Blade triggers once during this time period and that the beast gets full benefit of it (all 5 sec worth of enhanced damage). So.. (5 sec x 127) + (5 sec x 163) = 1450 damage. (this is best-case scenario)
This makes Hammer seem like the obvious choice, but Blade does have 2 additional advantages:
1. It gives +100 health.
2. Overall, it provides a higher average attack rate. Higher attack rates can be very useful for triggering critical hits and other big-damage effects (e.g. Slayer's Wraps, Nature's Reckoning, etc.)
Comments, mistakes, feedback?
EDIT (based on Sly's comment): The Scaling Issue
UB at Level 10, no other items or abilities:
Base UB damage/sec: 197/sec
with Hammer: 243/sec
with Blade: 207/sec --> 274/sec (triggered)
Blade will pull away the more damage-enhancing equipment you stack on UB. So, early game advantage to Hammer; late-game to Blade?