Wi-Fi is great but only if:
- It's properly configured based on your surroundings and neighbouring RF interference
- You're using half-decent gear
As you're well aware, the 2.4 GHz spectrum is congested almost to the point where it's unusable in built-up areas. If you're using your bog-standard consumer gear like D-Link etc... forget it. If you can utilise 5 GHz as opposed to 2.4 GHz, then do that, but I get that not all devices support the 5 GHz band.
It's a common misconception that if you can turn up the TX power on your Wi-Fi access point, you'll be able to "talk over" or "break through" the congestion. Nothing is further from the truth, in fact, in a lot of cases, it just makes things worse. A Wi-Fi radio won't transmit if it detects another station transmitting on the same channel, it will wait for an available time slot. To improve Wi-Fi coverage, you want to increase the gain of your antenna (either by using an external antenna on your access point, or using a better quality access point).
The automatic channel selection feature on most access points can be good and bad, depending on how it's implemented. You can use it to your advantage, for example by forcing your gear to use a fixed channel, you can essentially "push" your neighbours onto other channels (works better in the 5 GHz band). Some radios will only automatically select a better channel on boot, others will monitor channels periodically. Do a proper site survey (using tools like Wi-Fi Analyzer on Android) to see what's around you and pick the least congested channel, in my area Channel 13 is almost entirely free as many manufacturers prefer to default to channels 1, 6 and 11).
A mate of mine who lives in the Sydney CBD could barely even connect to his 2.4 GHz Wi-Fi using his ISP-supplied Netgear modem/router, let alone be able to use his connection. I swapped it out for an enterprise-grade Cisco access point which improved things immensely. Not only could he now connect, but he could actually stream Youtube in HD, something he was never able to even do in SD.
The other thing you can try is use a narrower channel width. I don't know why but some people are under the impression that using wider channel widths (like 40 MHz) in an already congested band makes things better, when it actually makes things worse. I think the default on 2.4 GHz is 20 MHz, if your access point and devices support it, try 10 MHz instead.