Masturbators are a great sex toy - especially for those who lack manual dexterity or are at high risk for repetitive strain injury.
The problem comes in when you look at the huge variety available. Strokers? Sleeve masturbators? Automatic or manual? Nothing to do with gear boxes, although there is definitely a stick involved!
Manual masturbators are operated, generally, by thrusting into the toy or sliding it up and down your shaft. Automatic masturbators use the same technology used in vibrators, or are designed to stimulate a blow job.
Which do you pick?
Manual masturbators tend to last longer - although some automatic masturbators use vibrating bullets that can be replaced. You don't have to worry about replacing or recharging batteries, which can be cheaper in the long run. They're often easier to deal with for guys who travel a lot and tend, at the current stage of technology, to be a little more compact. They also tend to have more variety in tunnel design - something which is very definitely a personal choice, but you may well find one masturbator works much better for you than another.
However, automatic masturbators can deliver a more intense sensation (although it can be too intense for some). And some of them are hands free, which is much more like being with another person than having to manually operate a toy. Some are designed to mimic a blow job, something you can't really do with a manual masturbator. Men who prefer automatic masturbators are generally, though, attracted to the completely hands free nature. Blow job stimulators are also handy for couples if one partner is really uncomfortable with doing fellatio, and some are designed to work in conjunction with a person. As a note, the batteries tend to run out quickly on automatic masturbators - rechargeable is better than replaceable. Either way, you can expect a much higher level of stimulation and true hands-free action with automatic masturbators.
The choice between the two is mostly personal preference - and really comes down to whether the hands-free action is worth the extra fiddling with batteries, and how much sensation you want. Price-wise, there is surprisingly little difference. A manual Fleshlight will run about $80 to $100, with the vibrating one only a few dollars more, and some automatic strokers are cheaper than manual sleeves, so cost is not a concern - unless you're thinking of the cost of batteries. It really boils down to which gives you the best experience - although one thing worth considering is that some automatic vibrators can also be used manually - and that might be the best compromise of all.