Spellcrafting can make a single set of equipment that maximizes all nine resists. Because it is difficult and costly to simultaneously maximize all of your resists, the “optimal” set of equipment for a given situation depends on what kinds of opponents you are most likely to face and what types of resistances are checked by these opponents damage output.
In PvE, prioritizing resists is usually very simple. Figure out what type of physical damage is being dealt by your monster by looking at the messages in your combat window and comparing them to your calculated effective resists (including your armors intrinsic resists). For example, if your effective slash resist is 39%, your effective crush resist is 20%, and your effective thrust resist is 10%, “Monster hit you for 61(-39) damage” tells you it is doing slashing damage, while 120(-30) would be crushing, and 99(+9) would be thrusting (as examples).
Once you know what type of physical damage a monster does, maximize that resist. A small fraction of monsters cast spells; you can usually deduce the resist type of the type by reading the messages (“searing heat” is heat resist, etc.). In the case where you are fighting casting monsters, maximize your physical resist and the appropriate magic resist.
RvR is a much more complicated situation. In general most of the damage I take is from melee attacks, but that is in part because I play a tank class (warrior), so your mileage may vary. Most of the melee attacks I face are piercing damage, followed by crushing and slashing damage. What about spells? The resist type checked by all offensive Hibernia and Albion spells is shown below.
Midgard spells:
Skald: DD Body, Mez Body, Snare Spirit
Shaman: DOT Body, Bolt Matter, DD Matter, DOT Matter, Snare Matter, Snare Matter
Healer: Mez Body, Mez Body, Slow Body, Snare Body, Stun Body, Stun Body
Runemaster: Snare Body. Bolt Energy, Bolt Energy, DD Energy, DD Energy, Snare Energy, AE DD Energy, DD Cold, DD Cold, Debuff/DD Cold
Spiritmaster: Snare Body, DD Spirit, Mez Spirit, Slow Spirit, DD Cold, Lifedrain Cold, Mez Cold
Thane: DD Energy
Albion spells:
Theurgist: DD Cold, Snare Cold, DD/Snare Cold, DD Spirit, Mez Spirit, Slow Spirit
Wizard: DD Heat, DD Cold, Snare Cold, DD Cold, Snare Cold, DD Heat, Bolt Heat, Bolt Heat, Bolt Matter, DOT Matter, Snare Matter, Storm Matter
Cabalist: Lifedrain Body, Slow Body, Lifedrain Body, DOT Matter, DOT Matter, Snare Body, Snare Spirit
Minstrel: Mez Body, DD Body, Stun Body
Sorceror: DD Body, Snare Body, Snare Body, Lifedrain Body, DOT Matter, DOT Matter, Snare Matter, Mez Energy, AE Mez Energy
Cleric: DD Spirit, Stun Spirit, DD Spirit, Mez Body
Hibernia spells:
Eldritch: DD/Snare Energy, Slow Energy, Snare Energy, DD Cold, DD Heat, Stun Heat, DD Cold, DD Cold, Bolt Cold, Bolt cold, DD Energy, Mez Cold
Enchanter: DD Heat, Stun Heat, DD Heat, Slow Heat, DD Energy
Mentalist: DOT Energy, DD Heat, Stun Heat, DD Heat, DOT Energy, Mez Energy
Bard: Mez Body, DOT Body, DD Body
Champ: Snare Spirit, Slow Body, DD Body
Nightshade: DD Cold
Druid: Snare Body, DOT Body, Snare Matter
Thus in order to prioritize offensive and defensive capabilities you need to study your enemies. The server population, class distribution and your most frequent targets will help you understand where to place your resists. My personal recommendations are
Offensive vs Albion: Use Crushing weapons vs tanks and assassins, thrust vs foes in chain. Alchemy procs should be Energy or Matter based.
Offensive vs Hibernia: Use Slashing weapons vs tanks, crushing vs foes in light armor. Alchemy procs should be Energy or Matter based.
Offensive vs Midgard: Use Thrusting weapons vs tanks. Alchemy procs should be Energy or Heat based.
Defensive vs Albion: Be sure to keep Body, Spirit, Cold as high as possible.
Defensive vs Hibernia: Be sure to keep Body, Energy, Cold, Heat as high as possible.
Defensive vs Midgard: Be sure to keep Energy, Body, Cold as high as possible.