I'll echo much of what's been said about Allen keys and hex-head screws. There is one advantage of Allen screws over Torx and Star-Key types and that's the fact that a ball-end Allen-key will allow you to get at awkwardly placed ones.
I've also often turned to an over-sized Torx-key hammered into a rounded Allen screw cap to free it.
As for the size of the drive, I've increasingly found that smaller is better for most things on a bike. I rarely use a ½ inch driver these days other than on large bolts/screws with a high torque value. Even a 3/8 drive is often too much and I probably use a ¼ inch drive as much, especially on the small stuff.
The usual Allen-key, a right-angled bar, is too hit-and-miss to trust. Fine for the tool roll as an occasional/emergency use but not much else.
One set of keys I have are T-handle with a ball-end. Apart from the ability to get at screws from an angle, the ball-end will often hold the screw on the tool while you start the thread.
One of these combination sets:
is very useful (and not expensive).
It has half-inch and 3/8ths adaptors and is much cheaper than buying socket keys in all the sizes needed.
It has other benefits too. All the keys are 10mm so you can slip a ring spanner on the shaft to get a good turning force on them if needed:
I often use a "speed" ratchet (¼ or larger):
Again, quite cheap. They do make those long screws where you are constantly having to remove the Allen-key every quarter turn because there's not enough room less tedious to deal with.
If more turning force is required, you can slip a 10mm ring spanner onto it:
I don't buy top quality stuff because I don't earn a living using my tools. The higher-end DIY/amateur stuff is good enough for me.
The internet has made buying individual tools much easier than it was. The days of buying combination sets and only ever using half of them is over for me. That said, I do have two of most things because in the past when I needed one size of tool on one end of a fixing and found that I needed another one on the other end, resorting to the "bodger's favourite" (adjustable spanner) usually ended in tears.
I'm (often rightly) accused of being anal because I keep my tools like this:
My excuse is that I can find what I need and more importantly I can tell if anything is missing and with the smaller tools I don't want anything left inside whatever I've been working on. Well that's my excuse and I'm sticking to it.