The problem with death is not "lugging around ten trillion potions to prevent it," it's "if you fuck up at all with using them, or, say, lag for five seconds while stuck among a mob while the game actually goes through using that potion" (fuck satellite connections for gaming, seriously) - less a matter in difficulty of preventing in optimal conditions, and more a matter of how harsh the punishment is when you screw up, whether it's your fault or not.
It also discourages exploring new and dangerous areas so heavily it isn't even funny, confining you to the same regions for ages... and sometimes insta-killing you if you stray out of the ones you can handle. Especially when quests require you to go through regions that you can't really handle.
Clerics make the best budget class, at least once you get to 2nd job or so; MP Eater+Heal = drastically reduced potion costs. They're also VERY party-friendly, if you have friends actually near your level or want to do party quests (and it looks like the rewards for doing a given one a ton are pretty good; well, pendents are rare, at least). They're downright unfair against undeads. The problem is that they're pretty crappy at fighting anything else, restricting their training options more than other classes... and being so unfair against undeads while having to only kill them means that they can get very boring. I'm also told they hit a 'dead zone' for training in 3rd job, since there's no good undead-hunting maps between that point and 4th job; this means either spending 2-3x as long at much weaker enemies, or being 'tethered to a warrior,' as he put it.
But they also get the "wtfsooverpowered:(" Genesis in 4th job, which is a stupidly powerful holy-elemental attack that hits the whole screen; highly desirable for slaughtering Skelegons on Horntail Mountain (the strongest undead in the game) or causing general havoc. Of course, it costs several thousand MP to use...
Also good about mages is that they're pretty easy to build, stat-wise; Thieves, Archers, and (maybe?) Pirates eventually need to sink some points into HP so that they can continue surviving the enemies they fight. Warriors get more HP than God and never need to worry about it. Magic Guard at least MOSTLY lets mages ignore this, though they'll have to spend about twice as much on 'healing' to restore the MP losses. Teleport is also fun, unique, and useful.
Assassins are also more fun to play early on; Lucky Stars' damage formula is stupid and broken but it's also more reliable than the 5-100% damage range for weapons that warriors, brawlers, and archers are stuck with until 2nd job. Throwing stars allow a lot of range and mobility, making it easy to keep moving and try to evade attacks with your own skill as much as anything. Haste is highly desired because the free speed boost makes the platforming aspect of the game more fun. It's the mobility that makes them fun, by and large.
On the downside, everyone will assume you're an asshole because assassins are also the most twinkable class: watk increases give disproportionate damage boosts since their weapons default as having very little and the formula is boosted to make up for that (I think?), despite the potential boosts from scrolling those weapons or other items remaining constant. As such, useful gear for them is expensive like hell, and expectations from others are through the roof as opposed to "ridiculously high because your standard MSer is an asshole."
