As always… the answer is: It depends. 
This because target selection comes more down to weapons and tactics rather than simply ship type.
For example:
- Your PvP-fit Ferox… is it blaster or railgun fit? Is it fast, more equipped with more “utility” / E-war, or is it a “brick?” Does it have a Microjumpdrive? etc.
If you were to fly a blaster-fit Ferox with a brick tank… you could pretty much brawl down most cruisers and battlecruisers that do not have an active tank. However you would probably not have the speed or utility to catch smaller ships.
If you were to fly a blaster-fit Ferox that is fit for speed and utility… you will have some issues brawling down tougher cruisers, but you may also have an easier time dealing with smaller craft.
If you were to fly a railgun-fit Ferox you will want to fit for speed and utility. And you will also want to avoid anything coming closer than 30-40km from you as your guns won’t be able to keep up with any ship at that close of range.
edit: Here is an example of an active-tanked, blaster Ferox (with a lot of implants and boosters) taking on a couple of cruisers.
It survives… but only because the surviving cruisers bug out rather than try to finish the job… which they could have.
For fighting Rattlesnakes…
- they use missiles and drones as their means of fighting.
- missiles apply damage by looking at a target’s signature radius (see: sensor footprint) and speed. The smaller the signature and the higher the speed, the less damage the missile will do.
- drones can be targeted and shot down. One can also apply E-war on them.
- the Rattler has an enormous drone bay. So unless you have a lot of time to kill and/or can expect that the Rattler pilot will NOT get backup, killing the drones is not viable.
- both drones and missiles do not require capacitor power to function
- a Rattlesnake, when properly fitted, can tank a metric fuckton of damage.
- Rattlesnakes are slow ships
With all this in mind come the questions:
- How is the Rattlesnake fitted? Active tank? Passive tank (see: regen tank)? Brick tanked?
– Each tank type means that the ship needs to be approached in a different way. - What kind of missiles is it using?
– Rapid Light Launchers hurt frigates
– Rapid Heavy Launchers hurt Cruisers.
– Torpedoes and Cruise missiles hurt large ships but are pretty useless against smaller ships. - What is the pilot’s kill record like?
- What hours does he/she operate in?
- Does the pilot operate mostly solo or is he/she the harbinger of a larger force?
So what options are there?
- Depending on the tank,
– against an active tank I would fit a ship that can drain or neutralize the Rattlesnake’s capacitor.
– against a passive tank… well… there is actually very little you can do against a passive tank besides apply neutralizers and HOPE that the shield hardeners are active and that you have enough damage to overcome the shield regeneration rate
– against a brick tank… it all comes down to how long can you last versus them. Fitting an active tank yourself may help give you the endurance you need… then again… the Rattlesnake can fit an energy neutralizer of their own to zap your capacitor and leave you with even less tank than before. - You will need some kind of ship with enough toughness and point defense to overcome the drones. A Rattler can launch 2 heavy drones, each with the hitpoints of a lightly tanked cruiser.
- Depending on the missiles used, you may want to opt for a smaller or larger vessel.
- Wanting to use range or straight brawling will also depend on whether the Rattler pilot likes to operate solo or not.