A common question among new players is what type of ship & fit they should fly if they're just starting to try out solo or small gang pvp. For gangs, it's a pretty easy answer: if there's a gang doctrine, you fly the ship the FC tells you. If not, then pick your favorite ship and go with it. Often your mere presence in the gang is much more valuable than having the "best" ship.
Solo is different. Each race has two combat frigates and one attack frigate. That's 12 ships in all, with tons of variations in fits among each. In 1v1 battles, it is nigh impossible for CCP to balance all of these ships perfectly, so naturally some are going to be better than others. Rather than rank all the ships individually, I've ordered them into five tiers (from best to worst). This is based only off my experience soloing in low sec for the past 4 months. Don't be mad if I think your favorite ship sucks, be happy that it's underrated!
Tier 1 (Best): Incursus, Breacher, Slasher, Condor
Tier 2: Tristan, Tormentor, Atron
Tier 3: Merlin, Kestrel
Tier 4: Executioner, Rifter
Tier 5 (Worst): Punisher
Tier 1 Ships
If you've read any of my other posts, then you know that I will extol the virtues of the rail Incursus to anybody who will listen. The Incursus is also a great brawler, capable of dealing a ton of DPS, and the famous dual-rep fit is deadly against the right target. Just a very versatile and effective hull. The Rocket Breacher is a top-notch scram kiter, while Light Missile Breachers are great MWD-kiters, which have the mid slots to spare for a tracking disruptor.
The Slasher isn't very versatile (artillery fits just aren't viable because of low DPS, in my opinion). However, autocannon fits with a neutralizer in the utility high slot are deadly against laser & hybrid ships. Slashers are so fast that they simply cannot be scram-kited unless you have two webs. They are the best at what they do, by a long shot.
The Condor is king of MWD kiting ships, and dual-TD/dual-damp fits are so effective that most people simply refuse to fight Condors. A great ship, but you might have a problem getting fights.
Tier 2 Ships
I almost made the Tristan a Tier 1 ship, and with max drone skills (including drone interfacing V), it probably is. The Tristan is ridiculously versatile, but it doesn't quite "excel" at anything. It can't be as good a brawler as a Merlin, MWD fits aren't as good at kiting as Condors, and AB/rail fits aren't as good at scram-kiting as a rail Incursus or a Breacher. Still, it is a great, great ship overall.
The Tormentor is the best option the Amarr have. I mentioned in an earlier post that Tormentors are good scram kiters that can double as decent brawlers simply by switching ammo. However, I'd rather be flying an Incursus in most situations. Tormentors are fairly slow, and they have no means to deal with long-range kiting ships (max range of Scorch ammo is only about 12km). The Tormentor also isn't particularly versatile.
The Atron on the other hand, works as either brawler or a longer-range kiting ship against many targets. It's biggest weakness is its low EHP, which means that it will get out-brawled by ships like the Merlin or Incursus, and kiting fits will die fast against anything that can hit them. Overall, I prefer flying Atrons as kiters (described in an earlier post), but I've found that they aren't able to engage as broad a variety of targets as a good scram-kiting ship. "Slasher-like" fits aren't particularly viable on this ship either, it simply doesn't have the capacitor or the slot layout to handle a neutralizer the way that a Slasher can. Flying an Atron can make you aware of just how powerful having a fourth mid-slot can be.
Tier 3 Ships
The Merlin is ranked alone in this tier. It has great DPS with blasters, excellent EHP, and it can scram-kite when fit with rails. The biggest problem: Caldari ships are just SO DAMN SLOW. In the current meta, soloing with a slow brawler just leads to a loss mail. Just about anything, and I mean ANYTHING can kite you. Every conventional Merlin fit I've tried just makes me wish that I was flying an Incursus instead. The reason I keep Merlins in my hangar is that armor-tanked versions are deadly against the right target. This opens up an extra mid slot for e-war modules. I have a dual-web armor-tanked rail Merlin that I fly specifically to counter brawling Slashers, although it isn't much good against anything else.
The Kestrel is almost a missile version of the Merlin. It shares a similar slot layout, hull bonuses, and slow speed. In practice though, it flies more like a worse-version of the Breacher in a solo context. The bonus it has to projection simply isn't as powerful as the Breacher's active shield tanking bonus, and rocket Kestrels aren't as good at scram-kiting as Breachers are. The only reason the Kestrel isn't a tier 4 ship is that light missile kiting fits are actually quite effective, although it's not as good as a Condor in this role.
Tier 4 Ships
The Executioner is clearly below average. Show me an Executioner fit, and I'll show you an Atron fit which is better. Most people seem to agree with me, because I hardly ever seen an Executioner flown by someone who isn't plex farming.
The Rifter is just not very good either. Artillery fits deal anemic DPS compared to small-railgun or pulse-laser fit scram kiters. At best, brawling autocannon fits are just slower versions of the Slasher. Fortunately, the Rifter is due for a major buff in an upcoming patch. Its tracking bonus will be replaced by a falloff range bonus, which will help artillery fits significantly, and widen the engagement profile for AC fits (they'll be able to scram kite brawlers like the Merlin). I believe this will elevate the Rifter to at least Tier 3, and certainly make it worth flying again.
Tier 5 Ships
The Punisher deserves to be in a class all by itself, because it really is just that bad. What do you call a slow ship, without a web, that has no DPS projection beyond 12km? A loss-mail waiting to happen. Any ship even remotely capable of kiting can kite a Punisher, and any brawler can simply run away easily if he's losing. Don't get me wrong, it's a good ship for a gang situation because it can have an excellent armor tank, but if you're soloing you're better off flying anything else.
You might notice that the Gallente & Minmatar ships are quite highly ranked, while the other races (especially Amarr) aren't doing so hot. I really think that this is unfortunate, I'd love to see every race have a couple solid options. I particularly feel for the newbie who starts off in a Punisher and repeatedly gets his ass handed to him, simply because he's flying such a bad ship. The Caldari don't have things quite as bad, but they do suffer from having two frigates (The Condor & Hookbill) that are so good that many people simply won't fight them.