Here is my two cents worth on HF. I've been listening to aircraft communications on HF for almost 30 years. My current receiver is a Yaesu FRG-8800. It's an old receiver but it does the job. I actually bought that receiver for the sole purpose of listening to the aircarft HF bands. In all those years I have only used a long wire antenna. This is simply a long length of wire that you connect to the back of the receiver and then run outside. I've got mine secured to the gutter of my house (insulated from the gutter of course) and a tree at the far corner of my yard. It's a very simple set up but it works quite well for me here in Long Island, New York.
With this long wire antenna I can hear NY Radio during the day on 6577 loud and clear. I can aslo hear Gander Radio on 8864, 8831, 8891 and 8879 during the day. The reception of Gander Radio is not that great during the day but with a better antenna, it would most likely improve the reception greatly.
At night it's a whole different story. Gander comes in loud and clear on 5616 and 5649. You can also hear Shanwick Radio and Santa Maria radio clearly at night too. Shanwick can be heard on the same Gander freqs as well as 2971, 2872, 2899, etc. Santa Maria can be heard on 5598 and 3016. Iceland radio can aslo be heard on 8891 (Gander can be heard here too) and sometimes on 4675.
But it goes even further than that. I can hear flights over Africa on 8894 and flights coming out of South America on 6649. San Francisco Radio can also be heard although that doesn't come in too well by me. But they can be heard on 5547, 5574 and 5643. The best time for this would be late at night or very early in the morning (well before sunrise).
So, even though I have a very simple long wire antenna, I can hear quite a bit. Someday I'll upgrade my antenna and receiver but for now it's ok for me. BTW, all the freqeuncies I mentioned are upper side band (USB) so whatever receiver you decide to get, it must be able to receive LSB and USB transmissions. A straight AM shortwave receiver won't work.
If you want to know anything else, let me know. Have fun!