What is the best way to mine bitcoin today?
By having "ASIC" mining rigs (lots of it).
Is it always profitable?
No, it's not. A lot come into factor when profit is the target, like electricity rate, having a miner that functions normally, the difficulty factor (that mostly goes up) and the possible repair fees that add up along the process.
You forgot about the possibility of a fire, theft, miners breaking due to surges, lightning strikes, or just component failure.
There's also an issue with transport, fees, the possibility of equipment being lost, stolen or damaged in transport.
There are also losses coming from downtime due to from network failure, so it's needed to monitor the miners 24/7. The Chinese, who are really serious about this business, basically live in their mines.