There is a lot of weird information here, it really isn't that complicated but it can be made to be.
Taking caffeine needs to be taken in small amounts over a period of time during a race not all at once before the race. Usually you take about 100 mgs of caffeine an hour before the ride then take 50 mgs each hour after that during the ride. I break it down a bit more than that, the GU flask is marked in 1 ounce increments, a one once shot of espresso is 40 mgs of caffeine, so I drink a half an ounce every half hour instead, not sure if my way works better but I think it keeps it more evenly balance in my system.
The problem with using caffeine is that your body can become tolerant to it if you consume it too much which means you'll need more caffeine to get the same effect you once got with less. You shouldn't be drinking more than a 1/2 a cup a day if you want to use caffeine as a training/race rides enhancer. I only drink espresso, Moka, French Press, or Cold Brew, but I use the demitasse cup and only drink one a day, some occasions I may have another cup if I'm at a resturant that has espresso, but that is an exception and not a rule, but by drinking a small amount in the day it doesn't build a tolerance to the coffee which will help you during training/race rides. And when you think about the dosages of caffeine I mentioned that is about what is in those gel type of products. Again like I said in an earlier post you can do the same thing those gels do for a heck of a lot less money by simply pouring black coffee mixed with about a teespoon of honey, which makes the coffee taste odd but it adds a slight boost to the caffeine in a different way that sugar does not, and in fact sugar will actually make you tired as you ride whereas honey does not because your stomach requires more energy to absorb sugar which in turn takes energy away from your riding.
Coffee is actually better for you then tea if taken in moderation, coffee protects the heart and protects against several illnesses. There are all sorts of things you can put in coffee, none of which I do because it makes coffee taste too odd for me, but you can put cinnamon in which is suppose to help with inflammation, but you have to use true cinnamon called Ceylon to get the benefits, I can't recall the mix ratio though because I don't do it. Coconut Oil is another thing you can add to coffee, Coconut increases metabolism and energy, but again I don't do this because I don't race so all that **** isn't important to me. I also heard to use grass feed cattle butter. Then you mix all those ingredients and add it to coffee...YUCK, and I mean YUCK! Those ingredients made my coffee taste nasty, it wasn't worth whatever gain I may see to do it more than once, and frankly I didn't notice anything different than just coffee and honey. Anyway I put the coffee (espresso) and honey into a GU flask and take it with me on rides.
If you're using caffeine to the point of getting the shakes you're either allergic to caffeine or you're taking way too much. Having the shakes while riding will drain your energy from physically shaking, add on top of that if your heart is racing from the caffeine and then you crank up your heart more by riding a near to max levels you could have a heart attack.
Tea is not a pure caffeine rush, though tea leaves may have more caffeine than coffee beans but tea is diluted quite a bit more then most coffee is and then you lose the benefit, and if you drink the tea to get to the point that coffee does you'll lose any race due to peeing all the time. Also most of the caffeine in tea leaves is left behind in the leaves after the tea is made! And that is why a glass of tea contains 1/2 the caffeine that a cup of coffee contains.
Also tea isn't necessarily better for you then coffee, read this for more info on this highly controversal subject:
http://www.webmd.com/food-recipes/news/20161223/coffee-vs-tea-is-one-better-health#1
Caffeine pills are not simulated into the body as well as liquid caffiene is, but the biggest danger with pills is that most people take too much which is detrimental towards physical performance.
Dehydration isn't a problem with caffeine. Using subjects who habitually consumed a relatively low amount of caffeine...equivalent to one, six-ounce cup of brewed coffee (100 mg/day; about 1.3 mg caffeine/kg), they found no detrimental effects of caffeine on 24-hour urine volume. (Armstrong, In't J Sports Nutr, June 2005) By day's end, the urine losses were similar whether the person consumed no caffeine or a high dose.
The effect on performance is about a 12% gain plus the effort was about 6% easier, and the larger tilt toward performance was for those that had to do short high energy output efforts, so with a longer effort there was less an effect, but those tests did not keep resupplying the body with more caffeine as I mentioned to do earlier. And like I said earlier the performance gains mentioned above were less noticable if the user was a daily user of caffeine.
Caffeine either in pill, coffee or tea can be upsetting to some people, giving them the runs, throwing up, or jitters after just a small amount; so you have to know your body, if you're not sure then start out very small, if you get sick wait a week and try it again at the same small amount, if you get sick then stop using it it won't work for you. The reason you need to try it twice is to eliminate something else you had that may have upsetted your stomach that first time.