I use lots of primes, lets review them.
Owens: good in tonnage based drops, otherwise not useful.
Raven: best support mech in game.
Osiris: decent considering the chassis.
Uller: wonky but great starter.
Puma: 'nough said.
Cougar: with each patch becomes more and more deadly.
Hollander: watch a KoS match and tell me its bad.

Uziel: best overall variant.
Buswhacker: trashy.
Scat: pinpoint damage like a boss.
Catapult: situational but tough.
Vulture: bad.
Thor: awesome but only good players use.
Loki: god tier.
Madcat: be afraid everytime LRMs get buffed.
Warhammer: god damn sexiest mech in the game.
Thanatos: garbage.
Novacat: best overall Ncat outside the JJF.
MKII: great but ammo dependent.
Awesome: Awesome.
Mauler: not what it used to be, best at combined arms warfare.
Atlas: Horridly underweight but best design philosophy of the bunch.
Fafnir: much better staying power than iHgauss ammo.
Basp: How can it be bad?
Let's review.
Bad - 4
Good - 13
Great - 7
I'd say that is pretty good. Not sure where this idea about non-boat primes being bad came from... its basically the broken/flawed ones that are bad. (lol worthlessly implemented weapons, total lack of heatsinks, laughably underweight)
EDIT: forgot hollander.