Guild Wars 2

How powerful is rare weapons and armor and trinkets in guild wars 2?

they’re not as good as exotics, you should try to use exotic berserker gear once you’re 80

Not as powerful as Exotic (orange) or Ascended (pink), but more powerful than Masterwork (green), Fine (blue) and Common (white).

For the most part you can use Rare armor and weapons and never have any issues completing the majority of content. Also, Rare are much cheaper than exotics. Would probably be a good idea to only pick up Rare armor and weapons until you hit Level 80 and then look to outfit with L80 exotics.

Also take note of the level of Rare items when planning out your upgrades.
As an example, you can easily pay 40 silver+ for a L39 Rare (when you can start using Major Runes/Sigils), but if you wait and get the L40 or L41 version then it might only cost 7s due to the demand for that level item being much lower. Can save a lot of coin by putting off your upgrade for a level or two.

Trinkets you can generally get by with Fine (blue) until L35 and then switch to Masterwork (green) or rare beyond that. You can always re-sell your Fine items as long as you don’t add/change the upgrade component which will cause it to become unsellable. Probably stick with Rare trinkets until L80 also. You can then save for Exotics, or even spend some Laurels from doing Dailies to get an Ascended amulet and rings. Or, if you are into WvW, you can get them with fewer Laurels by picking them up there with a combination of Laurels and Badges of Honor. But still probably only grab Exotic ‘accessories’ since the Ascended versions need Ectos in addition to Laurels.

http://wiki.guildwars2.com/wiki/Rare#Quality

Here is the chart of various offense rating for 5/5/2/0/2 guardian build with different gear quality set up:

Full Ascended Berserker: 4693.1
Full Exotic Berserker: 4310.26
Full Rare Berserker: 3906.9
Full Masterwork Berserker: 3724.73
Full Ascended Soldier w/ Power infusion: 3341.76
Full Fine Berserker: 3148.45
Full Ascended Sentinel w/ Power infusion: 2945.68
Basic Berserker: 2403.54

What does the offense rating mean?

To find the total dps of one full 10.1 seconds for greatsword rotation done to a 2600 armor target, multiply the offense rating by the following appropriate coefficients:

Ascended: 7.656585, Exotic: 7.291157, Rare: 6.462854, Masterwork: 6.003459, Fine: 5.561465, Basic: 4.440819

The following is the total damage for the full greatsword rotation

Full Ascended Berserker: 35933 (100 %)
Full Exotic Berserker: 31426 (87.46 %)
Full Ascended Soldier w/ Power infusion: 25586 (71.21 %)
Full Rare Berserker: 25249 (70.27 %)
Full Ascended Sentinel w/ Power infusion: 22553 (62.77 %)
Full Masterwork Berserker: 22361 (62.23 %)
Full Fine Berserker: 17509 (48.73 %)
Basic Berserker: 10673 (29.70 %)

Better than greens and worse than oranges and pinks

http://wiki.guildwars2.com/wiki/Armor#Defense_rating
http://wiki.guildwars2.com/wiki/Armor#Attributes