These are the four green-blue attackers in the game (not counting Thunderhead, because it's legendary, and Xeno Guardian/Urban Sentry and Chieftain, because they're primarily defenders). They all have one things in common besides being green-blue attackers: they're all high-pressure units that are good at high inflation (see my math article). Redeemer, Plasma and Tesla all deal massive amounts of constant damage in return for an additional cost to you, and Borehole Patroller gets a lot of its value from the Pixie - 6GB is a terrible price for just one permanent attack, but a great price for 2 damage immediately. This means the units are also better when there are other good attackers in the set, because the better the average attacker you're buying is, the higher inflation is. For Borehole, that's where the similarity ends, but the other three also share the fact of being heavy attackers (3-4 damage a piece and 4 supply). So you might expect that these 3 units and to an extent Borehole as well all play very similarly. You'd be right, but that doesn't mean there aren't differences between them. Let's talk about each unit individually.
Borehole Patroller is the least efficient of the four (1.38). This makes sense, because it's the cheapest. It's even less efficient than Tarsier (albeit barely). Nevertheless, the unit is about as strong as Tariser generally speaking, despite more being expensive also. Why is this? Well, let's count the advantages it has. For one thing, it doesn't cost red. Costing red is bad for an attacker because red is bad at defending, which is something that is important in every game (or at least every game where you buy red). For another, Borehole provides offensive finesse. The Pixie, even if it doesn't exploit your opponent, will often force them to make sacrifices to improve their granularity, and if you know about pseudo-exploiting from my fundamental principles of Prismata, you can manipulate your damage numbers to make it even harder for their defense to stay granular. If each third Patroller exploits for one, then it becomes more efficient than Blood Phage. That's a big difference. Finally, Borehole is a blocker. While you never want to use it for soak if possible, it can still be useful as an early absorber against your opponent first 1-2 points of damage or to defend against threat (since it's vigilant). That's three advantages. It has two disadvantages compared to Tarsier: being slightly clunkier, and lacking the buildtime, which can sometimes be taken advantage of to deny absorb or when your opponent already has a bunch of defense laying around. So that is why Borehole is often stronger than Tarsier in practice despite being both bigger and less raw-efficient.
Of course, I still haven't talked about when the unit is good. Borehole is rarely good to mass produce. It mostly sees play as a support attacker, not your main strategy but just a relatively efficient thing to spend blue on when you don't need defense. For this reason it's quite good with heavy blue units like Apollo or Defense Grid. And finally, like I said, it's very efficient when it plays around threat.
Redeemer is the second least efficient of the green-blue attackers (1.41). It's pretty weak after the nerf it got in the latest balance patch, but still winning for both players in base+1. Redeemer is slightly unique in that it's the only green-blue attacker that scales upward with good soak. You see, attackers generate damage, which is worth less if there's good soak in the set. And Redeemer is the same way. BUT, it also has part of its cost in the form of defense. That means that when you have access to better soak, Redeemer has a lower cost and thus gets better compared to other attackers (all attackers will get worse compared to Drones). Additionally, Redeemer is extremely well-suited to rushing down an opponent going for a high-econ build or a slow legendary unit like Zemora Voidbringer, because that means the opponent will have to focus on defense and won't be able to pressure you, and so the Gauss Charges that hit you will run in to efficient defense like Walls - maybe they'll even get partially absorbed. It beats the crap out of Savior.
The second most efficient of the bunch (1.46), Tesla Coil has a lot of drawbacks owing to the constant consumption of Engineers. For one thing, it means that every Tesla Coil you buy locks down 2 of your econ on buying Engineers for the rest of the game, which might make it hard to spend all your tech - and these Engineers don't get to provide granularity. Additionally, Engineer supply is a real thing in Tesla Coil games. Getting more than 2 is generally risky. It also makes it harder to maintain your defensive granularity, because normally you do that by buying Engineers, but if you buy Engineers just to use for defense, your Engi supply will run out even faster.
It isn't all bad news. This means Tesla Coil combos with units like Hellhound or Sentinel that will keep replenishing your Engineers. Also Electrovore/Galvani Drone, as the Engineers will still get to produce energy before they are consumed. Finally, Tesla Coil can choose not to attack. This can be good if the damage is being absorbed because it means you keep your Engineer, so Tesla Coil can be a counter to things like Plexo Cell or Polywall.
This is by far the most efficient of the four (1.54 recursively, 1.47 at Tarsier input - the other figures I've given have been recursive inflation). However, it scales down really badly with good soak, even more so than most high-pressure attackers. The reason is because it's a Drone saccer. At high inflation, Drones are worth a lot less, so units that sac them are better, which means inflation is higher, so Drones are worth even less... this is what causes Drone saccers to appear so efficient on a graph. But with good soak, BV is lower, so attackers are worse, so inflation is lower, so Drones are worth more, so Drone saccers are even worse... Nevertheless, even at Tarsier input it's more efficient than the other units are recursively, so it's definitely the strongest. It does have a major drawback in that the Drone saccing makes you more and more overteched as the game goes on, but it's quite worth it. Plasmafier also provides offensive finesse like Tesla Coil - it can choose not to attack if your opponent will just absorb the damage. This way you get to keep your Drone. Only it's even better, because Plasmafier actually blocks when it doesn't attack - how cool is that? With so much raw efficiency and these other advantages, this is the only one of the four that I want to see nerfed a bit - see my list of advocated balance changes.