Some people respond better to Adderall (mixed amphetamine salts) and other people respond better to Dexedrine (which is just straight dextroamphetamine).
Later doses (assuming you're talking about doses after the first dose [redoses]) will continue you to stimulate you and keep you awake longer, but there will be less euphoria. Every time you do this, however, the level of stimulation will be decreased until a point where your body's need for sleep overpowers the stimulant effects. If you ever get to this point, you're not using stimulants safely or effectively and need to take a break.
If you're talking about using Dexedrine for long workdays, then instant release formulations will be of even less help, as they only last 3-6 hours. You would have to take them a lot more often (read: more redosing...) to get the same effect. I don't recommend using the instant releases for your purposes.
In regards to your last question, I don't think any stimulant is better suited for your lifestyle, I think you need to change your lifestyle so you get more sleep (joking, well, only partially, I know you can't change your current situation).
Caffeine is an option, although it doesn't really work for a lot of people. I would avoid using any amphetamine formulation (Adderall, Dexedrine, methamphetamine, etc) if you can. If you have to use amphetamines, use them with respect, and try to take breaks between the days you use them, this will really help prevent your tolerance from getting out of control.