Antminer A3, to mine Blake 2b.
Note that this miner cannot mine bitcoin and you can't use it on Bitminter.
It may look like you will earn almost 11 BTC the first year if you mine Blake coins and sell them. The reality is that an ASIC for these coins will change everything, like it did with bitcoin in 2013. Noone will make as much as these numbers show now. If you had the only ASIC you would still not make that much. Because even your one ASIC miner would raise the difficulty. Still someone could make some quite good earnings in the beginning. Like it was with bitcoin. The people who got the first ASICs had some very profitable mining before the difficulty went up. In this case that's probably Bitmain themselves. By the time you receive the miner the difficulty will already be much higher than it is today. If you have one of the early orders you may still make a good profit - noone knows. At least Bitmain is not like Butterfly Labs that mined on customer ASICs until it was less profitable and only then finally shipped them.
I am new to mining and new to Bitminter. I am mining with my S7 in Bitminter pool for weeks but didnt received any BTC yet. I read that it pays when it finds block, but when?!
Finding a block is like a lottery. You can't predict when it will happen. With the current hashrate the average time for us to find a block is just under 2 weeks. We are working on getting the hashrate up. It has gone from 2 PH/s to 7 PH/s in a fairly short span of time. Hopefully we will have more frequent blocks in the future as our hashrate keeps growing.
Is Bitminter good for me with an old S7 should find another pool which pays faster? (I have to pay the electricitiy bill soon)
Whether you have an S7 or S9 doesn't really matter for which pool you should choose.
If you can't pay the electricity bill without frequent payouts, then perhaps you should mine on an extremely expensive PPS pool instead. While Bitminter is a very cheap pool to mine at, the payouts aren't at regular intervals. With PPS you pay extremely high fees, but you get paid regularly - and that is why you pay the high fees. If you have a PPS pool with 3% fee on the newly created coins and 100% fee on transaction fees, that's a total fee rate of about 28% currently. Bitminter has a 1% fee and optional donations to unlock perks, but you can turn that off.
Still, you may have to mine at 28% fee instead of 1% fee, because otherwise you are not able to pay the bills. Like they say, it's expensive to be poor.
What bigolin said is another option. You can do some high-fee PPS mining to ensure that you can pay the bills and put the rest on low-fee PPLNS mining.