Soul LinkersThere are a few types of linkers and Esma is one of them. In my opinion, Esma linkers are easiest to level, and of course, you will need to invest in Esma, Estin, Estun and Kaina. Esma linkers excel in PvM (against low MDEF monsters). They are not very good at WOE/PVP and mobbing. An alternative to leeching your linker is to level up your linker first (Esma or Battle type), then reset the skills/stat to a full support WOE linker. Most servers should have at least a Skill Reset as it's available on official servers using the Neutralizer. If you are unable to reset your stat points, just make a Hybrid.
"The most important links"?
That mainly depends on your Guild. For the purpose of WOE:
NOT USEFULHunter Spirit - none of the players in WOEs are "Beast/Brute" race
Knight Spirit -
Rebirth Spirit -
Monk Spirit - most Monks who WOE are spiritual monks. Thus, not much use.
SOMEWHAT USEFUL (Depending on situation/strategy)
Priest Spirit - A nice offensive. But, most priest in WOE are support type and have many other better things to do than Holy Light.
Super Novice Spirit - you don't see many Super Novices in WOE. It does have its uses.
Star Gladiator Spirit - NEVER greater than lvl1. All they need is a link, the duration of UNION is not dependent on the level of your link. Just cost a bit more SP for u.
Alchemist Spirit - Good for Berserk Pitcher skill
Sage Spirit - Essential for Hindsight Sage
VERY USEFUL (Depending on situation/strategy)
Soul Linker Spirit - if you have another SL in your guild/alliance. It can be very powerful.
Blacksmith Spirit - Full Adrenaline Rush will help boost ASPD
Assassin Spirit - Essential for SonicBlow Sin/ EDP SonicBlow SinX
Bard and Dancer Spirits - Essential
Rogue Spirit - Especially nice if your Guild Leader is a Stalker.
Wizard Spirit - Essential if your enemies have Kaite Linkers
Crusader Spirit - Ideal for Shield Saders
It's not always necessary to max links to lvl5. Some links are required as they are pre-requisites. You will not be able to max every link. Just choose those links which you will regularly use. If your alliance have 5 Wizs (full-time) and 1 Hindsight Sage (part-time). Its best to max lvl5 Wizard Spirit than maxing Hindsight Sage. Consult your guild leader/alliance and your other guild members.
References:http://irowiki.org/wiki/Soul_linkerhttp://write.ratemyserver.net/ragnoark-online-character-guides/mibus-soul-linker-guide/