hello

i want to buy asic miner with efficiency over the long run example 1year and especially with minimum investment
i want choose algorithm that algorithm's coins their difficulty do not get bigger in long time

plz help me for choose from this items:

innosilicon a8 cryptomaster

baikal giant b

baikal giant x

In my opinion a8 cryptomaster(no a8+) is best choise But with the arrival of more devices, it's surely less money(such as antminer x3)

thank you