Before adding investment in buying more miners, most people will consider which miner is more profitable and how to break even as soon as possible.
Generally, miners can be divided into the following types:
1) New published miners, and the currency it mines is generally mined by GPU miners, and those miners' hashrate is much higher than the GPU miners: for such kind of miners, the first batch buyers usually can get very high mining profit though the profit will keep dropping with more miners coming in. Those first batch buyers can generally break even in a short time.
2) New published miners, and the currency it mines is generally mined by GPU miners, and those miners' hashrate does not have big different with the GPU miners: for such kind of miners, its mining profit may be very similar to those GPU miners and it takes time to break even.
3) Commonly used miners in the market: such miners' mining profit has been on a comparatively stable status, though may still decrease slightly. It takes time to break even.
We suggest you to refer to "Mining Profit Estimate" function to consider which miner is more profitable and which miner to buy.