I use a modified carom taper for pool - the taper is Schuler Cue's European taper, which is a conical taper with some "relief for the fingers" (as Ray Schuler described it) in the first few inches. He designed this taper for Raymond Ceulemans, the great billiard champion. I don't know how long Ceulemans used this taper, but he did use it for a while at least. The tip diameter is 12mm.
In other respects, my cue diverges from what billiard cue purists would consider a billiard cue. It's 57" long (too long), 19.25 ounces (too heavy), and it doesn't have the wood screw. It's perfectly fine to play billiards with, though.
The carom taper hits very solid and I prefer it, but then I'm used to it. When another pool player hits with it they notice the difference immediately and generally they don't like it. As far as I'm concerned you can play pool with this type of taper just as well as with the near universal "pro taper", but others will disagree. Earl Strickland, for example, saw it and said "you shoot pool with that thing?" He did admit, though, that it hits very solid.
For pool you don't want a short cue like billiard players use. They seldom have to stretch for a shot because they have to hit it hard enough to hit three or more rails and stretching makes this difficult, but pool players often stretch for short soft shots. I recommend at least 57", 58" is probably better.
The "relief for the fingers" (a somewhat slower taper) in the first few inches is important to me. I also have a purely conical taper and I don't like it for pool. Maybe I'm just not used to it, but I see no good reason to try to get used to it.
