My favorite party to play around with is...
Warrior
Sage
Thief
Paladin
I prefer the sage over the priest just because of the offensive spells sage learns. You've got the zam and boom line of spells. Plus Sage also learns Kazing, which 100% of the time brings a party member back to life. If a fight with a boss is really close, you don't want to be rolling the dice with zing, will it work, will it fail? Sage's ability tree also has Disruptive Wave - you might have seen a few bosses already use this on you. I mostly use this for bosses that like to up their tension. Nothing worse than the boss keep psyching themselves up every turn and suddenly you are dealing with a 100 tension boss ready to cast a spell over your whole party. Disruptive wave will drop their tension back to zero and remove any buffs they have as well.
The only thing priest has over sage is Omniheal, which fully heals every party member to full HP. The downside with Omniheal tho is that it costs something crazy like 120MP to cast, that's a lot of MP down the drain. If you do the quest to get the sage scroll, you can cast Twocus Pocus at the beginning of a fight (16MP) which will cast any spell 2x. If your sage is set up with that, just do 2x Multiheals (32MP) and it's basically equal to Omniheal, all for the cost of only 48MP total. Twocus Pocus will also allow you to cast 2x attack spells like Kaboomle (~500HP damage), or 2x kabuff/magic barrier (full party protection of physical attacks/spells) all in one turn.
Sage's special ability tho is the spell they learn near level 80 called 'Magic Burst' - It's an attack spell that uses up all remaining MP. So if you have 400MP, it'll use that, multiply it by 1.5 and attack a boss for 600HP of base damage.
But it seems kind of stupid to use up all your healer's MP, which is where the Sage's coup de grace 'Spelly Breath' comes in as it restores lost MP. So before casting Magic Burst, be sure to have the sage CDG ready to fire. Magic Burst one turn, coup de grace the next. You've unleashed a powerful attack and then get most of your MP back. It's kind of a great big 'FU' to the boss. :lol
It's great to use this in combination with the Paladin's abilities as well. Unleash the Paladin's Coup De Grace which blocks ALL incoming attacks directed at them. And every turn thereafter use 'Forbearance' which has your paladin step in the way of every single attack for the whole party. Basically it buys you several rounds of freedom to do whatever. Completely heal your party, buff everyone out, magic burst, spelly breath. Boss is going nuts as nothing is getting through, you are buffing your party, attacking him, basically unleashing holy hell for a bunch of turns free of charge.