Just remember that, from an equipment burden point of view, Havel's Ring has a 30% advantage over the other ring (50% versus 20%)... though the added HP and Stamnia could also make up for this.
It really depends on your equip burden versus the equipment you have. If you're not wearing super-heavy armour or have almost enough END to use it all, then you should be okay with the RoF&P. Otherwise, Havel's Ring will pretty much be necissary.
Just remember that, if you decide to equip the RoF&P, you will have to commit to it. Once removed, it's gone until the next playthrough.
I put on the Ring of Favour at the beginning of the game and haven't taken it off, nor do I plan to ever take it off. The 20% equip burden is a cherry on top of 20% Health/Stamina.
You could always wear Havel's to maintain <50% Equip burden for moderate mobility, or if you can maintain <50% Equip burden with just Ring of Favour and your Armour/Weapon choices, just equip the Dark Grain Ring and you'll have the highest mobility + Ninja Flips. --- PSN ID: CrimsonSamuraiX MH3 Name: Crim 23U6QJ
I've been using the Ring of Favor and Protection in addition to the Dark Wood Grain Ring, with the Grass Crest Shield +15 for stamina regen. Works like a charm as the extra mobility allows me to go two handed while still taking minimal damage.