What determines how fast you revive someone in Guild Wars 2

Revival and it's speed is based on several factors:

1. Your health when you are reviving someone (Faster when you have more health to give)
2. Your experience level (More Experience = More Health to start with)
3. The number of people helping to revive the downed player (Revival is the sum of all people working to bring you back)
4. If the player you are reviving has a "downed penalty" (Slower recovery time and reduced per person revival

A player will "Rally" when 25% of their overall heath has been returned to them either through player revival or other skills. You also gain a little experience for reviving someone.

The easiest way to see the difference starting with more health makes is to head to PvP and do the Revive a Player Heart Task. Since you are automatically set to level 80 when you enter you can see the per second revival stat at it's maximum vs when you go back to PvE and it adjusts to your Health/Experience combo.

The Revival page on the wiki talks to the process but not so much the exact per second calculation.

The difference in number that you're seeing is because you will revive other characters approximately 3x as fast when you're not in combat compared to when you are.

The amount healed with each "tick" depends on that character's maximum health. Dynamic level adjustment keeps this fairly consistent between players and NPCs within any given area.

A character will be revived from either downed or defeated state when their health reaches 25% full.

Other players or NPCs can help you revive the downed or defeated character, and that character can also help with skills such as Bandage if they are merely downed.

There are also certain runes and traits that can speed up revival, such as the Fast Healer trait or a Rune of Mercy.

I don't think there is an effect to enhance the time, I think it's a standard time frame. As mentioned by Raven though, it does get quicker the more people who help.

I think this is to maintain balance with skills like Signet of Mercy and Glyph of Renewal otherwise it would making taking a rez skill quite pointless. More Revive skills.

I've also noticed that the time frame is the same and the % of health is what changes, so healing a lv5 you might get ticks of 8hp but on a lv23 you'd get a few hundred.

My experience was that the time taken to revive someone was standard, and the only way to do it faster was to get a second person helping. I also found that the amount of HP trickling in per tick was scaled off the max health of the target being revived. Some things got 50+ a tick, some lowbie NPCs got 5-7.