What are the differences between the four exploration frigates?

I am wondering what is the different between the 4 exploration frigates? Is there any clear advantage for one over the other?

Which do most people use?

There's no best, but similar to other ship classes they provide different bonuses and advantages/disadvantages.

I'm not really sure whether you're referring to the T1 frigates with an exploration bonus or the T2 CovOps frigates, which offer stronger bonuses.

Either way, the short answer is quite simple: Pick the exploration frigate that fits your starting faction, especially if you're new, because this will save you some skill time for now.

The long answer (as well as long-time answer): It depends on personal preferrance.

• Both, the Magnate as well as the Imicus are made for armor tanking with the Magnate being the lighter (read: faster) platform, while the Imicus offering more drone bandwidth (up to 4 light drones instead of 3) in exchange for speed (it's the slowest frigate in this category)
• The Heron is a shield tanked frigate offering a balanced ship.
• The Probe is the fastest T1 exploration frigate and can be tanked either way (shields and armor having the same strength).

Which one to pick? Up to you. While exploration frigates are often untanked (they're more about avoiding fights or getting away before being shot), some tank fitting your skills won't necessarily hurt. Despite that, you'll usually need at least two medium powered slots for your exploration modules. Keeping that in mind three out of four frigates can be a good choice, with the Magnate having a slight disadvantage.

Their T2 counterparts, Anathema, Buzzard, Helios, and Cheetah further build on these strengths and weaknesses (although with some shifted focus, e.g. the Cheetah being an armor tanked ship and only the Helios is able to field a single light drone).

EVE Online: Rubicon also introduced the Astero as a new exploration frigate provided by the *Sisters of Eve** faction. Although having similar exploration bonuses, this ship isn't really recommended for new players. It requires multiple skill lines to master (e.g. Amarr Frigate as well as Gallente Frigate, Small Energy Turrets as well as drone skills) and it's not really cheap to obtain.

If you'd like to read more about exploration as introduced with EVE Online: Odyssey as well as starter tips and more details about the different ships being available, you can have a look at this article on the EVE University's wiki.

I'm going to assume you're talking about the four T1 exploration frigates: Magnate (Amarr), Probe (Minmatar), Heron (Caldari) and Imicus (Gallente). The T2 covops frigates are really a somewhat more complicated question.

Let's assume the following:

• We will target lowsec and nullsec data/relic sites. The answer for highsec is "any".
• We assume you do not 'live' out in lowsec/nullsec, and need to get your haul back to hisec to sell it yourself.
• Wormhole sites and ghost sites involve combat with rather unfriendly NPCs... so we're not targetting those.
• Every module is chosen either to help us scan, hack, or escape hostile players.
• We are not fitting any weapons or tank. The assumption is that we will only try to escape from all fights, and we're very blappable.

Your basic exploration fit for lowsec/nullsec is below. Basic equipment is on the left (lowsec), and your upgrades are on the right (nullsec).

[Probe/Imicus/Heron, Basic Explorer]

[High Slots]
Core Probe Launcher I w/Core Probes   -> Core Probe Launcher II w/Sisters Core Probes
Prototype Cloaking Device I           -> Improved Cloaking Device II

[Medium Slots]
Upgraded 1MN Microwarpdrive I
Cargo Scanner I
Data Analyzer I                       -> Data Analyzer II
Relic Analyzer I                      -> Relic Analyzer II

[Drone Bay]
Warrior I                             -> Hornet EC-300

Note that with the Improved Cloak and MWD you can execute the "MWD+Cloak" maneuver to escape gate-camps. The drones are disposable... either a distraction or jamming until you can warp away. For rigs, choose among the following:

• Small Memetic Algorithm Bank - Data site "coherence" bonus (health in the hacking game)
• Small Emission Scope Sharpener - Relic site "coherence" bonus
• Small Gravity Capacitor Upgrade - Improve Probe Strength, use it if you need it

Your Low Slots are generally filled with one of the following three:

• Expanded Cargoholds - T1 exploration frigates have big cargoholds, but long treks in null are long.
• Warp Core Stabilizers - More useful in low than null (where you'll bump into more bubbles than tackle frigates)
• Nanofiber Internal Structures - Improve your align time, makes you much harder to catch, and makes the "MWD+Cloak" trick work a bit faster
• CPUs - Needed on some ships to fit the other modules (Heron is prone to this)

Now, to your actual question... "are there any advantages of one over the other". The simplest answer is "fly whatever you have the highest frigate skill in", since the hull bonus to scanning and hacking will tend to dominate this discussion. But there are some particulars to be aware of.

• Probe and Imicus are fine... basically identical ships that can be fitted easily with the above setups. Toss a Salvager I into that spare high slot (who knows, you might stumble on something, and they're cheap) Imicus has slightly more CPU, so if your fitting skills are crap, that might be a factor in the decision.
• Heron happens to have an extra medium slot. This probably makes the Heron the best T1 exploration frigate, since that slot can buff your probe scanning (Scan Acquisition/Rangefinding/Pinpointing Array)
• Magnate is slightly gimped by the lack of the 4th mid slot. This forces you to use one of the following options:
  • In Lowsec, only fit either data or relic, refit at a station when you want to hack the "other one".
  • In Null - drop the data module: Nullsec relic sites are typically better isk/m3
  • In Null - drop the MWD: This is living somewhat dangerously, but it somewhat depends on where you live/work.