If possible, I would suggest getting an actual Ethernet cable run from your gateway device to whichever room you're having trouble in.
In my particular case, I had a side of the house that got horrible signal attenuation due to the way the house was wired. To resolve this, I opted to have the ISP install two RJ-45 jacks (one next to their gateway device, and another in one of the rooms on the other side of the house) and run an Ethernet cable between them. They charged 70 USD for this service. Then, I installed another wireless AP at the far end of the cable and was done with it.
Theoretically, powerline should make you more secure than any wireless networking would be, because it mostly puts your signal on a physical medium rather than putting it out on the air. That said, it may make you more vulnerable to sniffing by those in very close physical proximity - either individuals who can plug into outlets on the same circuit, or who can get close enough with the proper equipment to analyze the RFI emitted by the powerline network. If the firmware offers any means (I'm not familiar enough with these setups to know) of signal encryption, definitely use it.
Of the options presented, here's the preference order I would recommend, with security as the highest priority. I place the wireless range extender above powerline without encryption, because I personally trust wireless encryption above an unencrypted powerline network. Always bear in mind that whatever encryption you put in place on the powerline or wireless network segments, will not carry over to the other segments of the network.
- Ethernet cable extension.
- Pros: Nominal RFI, minimal latency, highest security, nominal signal leakage
- Cons: Requires drilling holes, exclusive point-to-point connection
- Powerline network with encryption (if available).
- Pros: No holes required, low latency, high security, expandable
- Cons: Moderate to high RFI, moderate to high signal leakage
- Wireless range extender, using WPA2-AES security.
- Pros: No holes required, reasonable latency, high security, multi-user service
- Cons: Sensitive to RFI, high signal leakage
- Powerline network without encryption (if encryption is unavailable).
- Pros: No holes required, low latency, expandable
- Cons: Moderate to high RFI, lower security, moderate to high signal leakage