Since the release of bitcoin in 2009, the amount of hashing power available throughout the bitcoin network has grown exponentially. As a result, the process of mining has evolved to the extent that consumer grade hardware found in most computers these days is no longer sufficient to turn a profit.
When bitcoin first launched, the network difficulty was so low that it could be mined using any semi-powerful consumer-grade CPU. However, in 2010, the shift to GPUs (graphic processing units) had to be made as the amount of hashing power offered by CPUs proved to be insufficient.
Today, large-scale bitcoin mining operations do not utilize off-the-shelf hardware such as CPUs and GPUs anymore. Instead, a specialized piece of hardware, named Application Specific Integrated Circuit (ASIC), is used as it is purpose-built for the SHA-256 algorithm that bitcoin mining employs.
Given that ASICs and hashing power are a relatively niche topic of discussion, even within the cryptocurrency ecosystem, it is often difficult to discern between the different types of bitcoin mining capable hardware available.
Early ASIC miners included the Bitmain Antminer U1 that interfaces with a computer via USB and is capable of approximately two gigahashes per second. Even though it can be purchased online to this day, the cost of electricity will far outweigh any and all profits made by this thumb-drive sized miner. At a price of nearly $100, the Antminer U1 was sorely underpowered at the time of its release in 2014 and is absolutely useless four years later.
The Antminer U1 is not alone in this regard. The Antminer U2, Gridseed Orb, and Antminer S1 are all several years old at this point, rendering them obsolete and near worthless except, at least, under conditions where electricity is somehow free. Even then, a single Antminer S1 can only generate about $130 worth of bitcoin in an entire year, with that number expected to drop as the difficulty rises continuously.
The only profitable ASIC miners currently on the market then, are the Antminer S7, Antminer S9 and the Avalon 741. Out of these, the Bitmain Antminer S9 is universally considered to be the most powerful of the lot at 13,500 hashes per second. It is also, by far, the best value purchase out of any other bitcoin other available. Taking into account the US median energy cost of 13 cents per kilowatt-hour, the net annual profit made from one of these machines is just over $9,000.
The S7 and Avalon 741 are also decent options but are far less profitable at around $3,000 and $4,000 annual profit respectively. There is also the WhatsMiner M3, produced by Chinese firm Pangolin Miner, which is cheaper than the S9, but costs less, meaning you may see a return on investment in the same timeframe. The WhatsMiner M3 also has the longest warranty (180 days) out of any machines mentioned here.
Finally, there is the DragonMint 16T, where preorders were being taken for March 2018 (you now have to join a wait list) and claims to be the world’s most efficient Bitcoin miner. You will have to order five machines at minimum, and comes with six months warranty.
Before pulling the trigger on purchasing a mining rig though, it is important to consider several other factors associated with running a power-hungry machine 24/7 indoors. Even though the physical footprint of the miners may be relatively tiny, they tend to output huge amounts of heat and noise. It is not recommended to set up such machines in confined areas that are regularly inhabited such as college dorm rooms. That said, for regions experiencing extremely cold weather during winters, these machines can double up as very effective space heaters too.