Here is an example of the difference in stats between the complete sets:
(Items that are an absolute upgrade in terms of stats have been omitted)
So when you are finally in full 493 tyrannical gear you will have:
1530AGI = ~7% dmg increase
2287STA = ~6% health increase
1.23% Mast = ~0.57% dmg increase (based on 46.7% of enh dmg being elemental)
1.08% Crit = ~0.93% dmg increase (based on 16% > 17%)
1.04% Haste = ~0.55% dmg increase (based on 53.3% physical and not including additional maelstrom stacks generated by +haste and only casting at 5 mw stacks)
-1.71% power and -1.46% resilience = 3.17% less damage when hitting a full malev geared player.
Total damage increase = 9.05 - 3.17 = 5.88%
Theoretically the stamina increase is a defensive increase of ~6%, practically it allows you to survive one extra non-crit spell or ability. The practical side of stamina is most important here as in a pvp situation such as an arena, the only time the extra stamina gains relevance is when the healer is able to top a player off with unexpected healing crits that don't overheal the targets hp. This is very rare because a healer cannot predict when a heal is going to crit, nor is it a good idea in pvp to always aim to maximise healing efficiency. The relevance (or lack) of the extra stamina is especially noticeable when a team is going for the kill as the healer is often CC'ed when the target reaches killing range (~50%) hp.
Armor = 1% reduction in damage taken, but when we look at the top 50 3v3 arena teams from a random battlegroup (in this case, stormstrike) 42 out of the top 50 teams are either double caster or hybrid comps and a further 2 out of the remaining 8 include ret paladins who are hybrid damage dealers (both spell and physical). So, assuming your aiming for the top 50, armor is a 1% damage reduction 12% of the time, 0.5% reduction or, worst case 0% reduction the other 88% of the time.
TL;DR: Starting from full 476 gear: Upgrade items not included on the wowhead link first (above) (weapons asap), followed by everything else except the pvp medallion, which gets upgraded last.
As a final note: a higher AGI stat will make you burst higher inside trinket phases than equivalent pvp power does, so a 493 Tyrannical Geared player will be more 'bursty' than a 476 Malev. Geared player.