Picking a pool cue is a bit like getting married, you are going to be around each other for a long time, so pick a cue you like and can get along with. Also the pool cue is a good looking piece of kit, at least it is usually. The type of pool cue you have will depend on the type of pool game you are playing. For English pool the cue has a tip size of 8-10 mm depending on preference with the pros favoring the smaller 8 mm tip which can be tricky to use for a novice. Whereas the American style of pool uses bigger cues with bigger tip sizes, typically 11-13 mm in diameter.
The English pool cues are basically the same as for snooker, as the ball sizes are very similar with 2 inch for pool and 2 1/16 inch ball size for snooker. The tip sizes are 9-10 mm for both kinds of cue with some tip sizes going down to 8 mm for some of the pool players. They are often made of ash as well, sometimes maple and there are even pool cues made from titanium! But these are expensive and a simple ash cue would be sufficient. The cue usually splits in two for ease of carrying and whereas the popular split is ¾ for a snooker cue it is generally 50/50 for a pool cue as there is no need for extensions etc on a 7 foot table, the only extension you might need is a small 6 inch extension that screws in the but of the cue.
The American pool cues are somewhat heavier than their English pool counterparts and are usually much more lavishly decorated, often with linen thread wrapped around the lower end of the cue for the handle and they look like works of art. Indeed some of them have become collectors pieces especially the cues made by some of the famous cue makers like Balabushka, with cues changing hands for thousands of dollars.
The American pool cue usually comes in at 19 to 20 ounces with and some cues have a system for adding extra weights in them so you can tune the cue for whatever weight you want. Basically metal washers at 1 or 2 gms each are added to increase the weight. Also nearly all American cues are made from maple, with Americans preferring the cleaner paler look of that wood to ash.
I love the looks of American cues especially the linen wraps which are quite practical as well preventing sweaty hands slipping on the cue, but I play English pool most often and I wish they would produce an American style cue for the English game, the best of both worlds for me. But pick one you like the look of and remember the most important part of the cue is the tip, make sure it has a regular dome shape and plenty of chalk and look after your cue cleaning it often and like any good marriage you will not want to be parted with it ever.