What you plan to do with your new connection plays a massive part in which to opt for. If for whatever reason you want to throw around a lot of heavy-duty file transfers nothing can touch Gigabit for its speed. The downside is you have to have hardwired CAT5 or CAT6 cabling in place between every machine. If you can meet that criteria then welcome to 100MB/s transfer city, it's a lovely place to stay.
More likely is that you're going to opt for the powerline or wireless solutions. With both of these you're going to want to keep bandwidth requirements at the back of your mind. But just how much do you need?
The short answer for most applications is not that much. Take 'super-fast' 20Mbps broadband; that's a mere 2.5MB/s, which every powerline adaptor can handle the full-load of without breaking into a sweat.
Equally for online gaming demands are very low; for instance, World of Warcraft uses a miniscule 2KB/s while the more demanding Call of Duty 4 averages around 75KB/s peaking to 150KB/s. A bigger issue with online play is latency, but even here the addition of a 4 to 6ms delay isn't too awful in the grand scheme of things.
The biggest strain on a wireless or powerline connection is the streaming of media around the home. We can discount audio, even high bitrate audio at around 320Kbps is only going to consume 40KB/s. The big issue is video; not only does the connection need plenty of bandwidth for the stream, but it also has to be reliable and have enough overhead to absorb any drop outs.
At the low-end a good SD DivX runs at about 1,200Kbps, which is no more than 150KB/s, again no problem. Move up to a good quality 720p HD stream with DTS audio though, and this can be 6,000Kbps, around 750KB/s. Jump to 1080p with DTS and it's more along the lines of 9,000Kbps or 1.1MB/s. At the far high-end you could stream a raw Blu-ay rip running at 36,000Kbps, which will consume around 4.5MB/s.
At this point we're starting to hit the limits of powerline technology and 802.11n under certain circumstances. Even at this extreme end all the solutions on test are up to the job, if that's the only stream on the network.
Considering the price drops in both powerline and wireless kit it's possible to upgrade your existing network for about £100 to handle such uses. Of course, a Gigabit network will handle multiple HD streams, if you can get your better half to agree to a little wire play.