I know that in 3.x (including Pathfinder) it's common to talk about different tiers of classes in terms of power and versatility. Does this also apply to Starfinder, and if so, what are they? I rarely play with serious optimizers, but it would be nice to know if there are "trap" options that will leave one character feeling useless most of the time. (Yes, I do have the book but historically I'm a sucker for flavor and don't realize I've made an underpowered character until too late, and with a new game I wouldn't want that to happen to me, or to one of my players if I'm GMing.)
What are tiers?
Tiers are a ranking of how "powerful and/or versatile" the various 3.5 base classes are, with low numbered tiers being considered more capable than high numbered tiers. It's important to remember that certain caveats apply to the rankings:
- Tiers assume similar levels of optimization. Someone playing an optimized "weak" class (like a fighter) and using its abilities well may be a lot more effective than a poorly built wizard played by someone who doesn't know how to make use of its options.
- Tiers attempt to describe power over levels 1-20. Classes will generally be in their listed tiers immediately, though the gaps between tiers tend to be a bit smaller at lower levels.
- Tiers are based on published material only. Homebrew and house rules can and will modify the rankings of some classes or even just negate the entire ranking system.
- Tiers are based on relatively high-magic games. In a low-magic setting the rankings will be mostly the same, but the gaps between tiers will get a lot bigger, because magic items tend to be the best way for less powerful classes to cover up their weak spots.
- Tiers look at characters' ability to solve problems of any sort, not just combat.
We frown on link-only answers, so I'll go ahead and summarize the full tier list of all published classes, originally from here. Fuller descriptions of why each class is in its tier can be found here.
Tier 1: Wizard, Cleric, Druid, Archivist, Artificer, Erudite (Spell to Power variant) — Can do anything and everything, often better than lower-tier classes that supposedly specialize in that thing.
Tier 2: Sorcerer, Favored Soul, Psion, Binder (w/ online vestiges), Erudite — As powerful as tier 1, but no one build can do everything.
Tier 3: Beguiler, Dread Necromancer, Crusader, Bard, Swordsage, Binder, Ranger (Wildshape variant), Duskblade, Factotum, Warblade, Psychic Warrior, Incarnate, Totemist — Good at one thing & useful outside that, or moderately useful at most things.
Tier 4: Rogue, Barbarian, Warlock, Warmage, Scout, Ranger, Hexblade, Adept, Spellthief, Marshal, Fighter (Zhentarium variant) — Good at one thing but useless at everything else, or mediocre at many things.
Tier 5: Fighter, Monk, Ninja (both CA & Rokugan versions), Healer, Swashbuckler, Soulknife, Expert, OA Samurai, Paladin, Knight, CW Samurai (with Imperious Command), Soulborn — Good at one rarely applicable thing, or mediocre at one thing, or simply too unfocused.
Tier 6: CW Samurai, Aristocrat, Warrior, Commoner — Objectively worse at their specialty than another (often Tier 5) class, without anything else to show for it.
Tier 7: Truenamer — Apparently received no actual playtesting, mechanics as written simply don't work. See this question for more details.
There are detailed rules for parties with multiple ships now that the Starfinder Starship Operations Manual is available.
The previous answers to this question are well done, and they were accurate; however, they have been overcome by events with the Fall 2020 publication of the Starfinder Starship Operations Manual. This rules expansion contains a section on what is called "Squadron Play," in which the party is allowed to have as many as one starship per character. It contains detailed rules on how to balance the tiers of multiple ships, upgrade them whenever APL increases, and how to create "HQ ships"--large ships in which smaller ships can dock so that the players can interact face-to-face, travel long distances together, spend down time, etc.
In addition to rules on building and balancing multiple ships for a single party, the section also details new crew actions designed for cooperation between multiple ships in combat, such as flanking and flying cover for a wing man. There are also new starship upgrade systems designed for multiship parties, including a system that allows multiple ships to fuse together into a single large ship and break apart again into the constituent ships.
The book also has a section on armada combat, which is basically mass starship combat in which each player can control entire units of ships. Armada combat is for specific engagements in which the player characters find themselves taking military leadership roles, not for long term campaign play--which I believe is the kind of multi-ship party the original question was asking about.