I have a masticating juicer (Omega J8003) that I use an average of twice a week. Sometimes I'll juice a lot for a week or two and drink 2 mason jars full of random juice combinations a day, half the time with baby spinach, kale, or other greens as the base. Some fresh herbs work well, too, but you have to be careful not to use too much because they can be strong in flavor. I make a decent amount of carrot juice, too, in addition to apple juice, orange juice, and other pure juices. It's fun to play around with combinations, though, and ginger-based shots" are pretty good if you are feeling sick, as is beet.
When I got the juicer last year I was replacing 1-2 meals a day with juice for about 2 months straight, trying dozens of different combinations of juices. Very fun to experiment. My energy level was through the roof at that time. It helps if you aren't consuming caffeine (withdrawal/crashes will negate some of the energy you get from juice... and you won't need the caffeine if you are drinking a fair amount of juice) and have a healthy diet. If you are just drinking a cup of juice a day on top of eating a lot of fast food or junk food it's not going to do much for you.
I would be juicing more now than I do, but it takes a decent volume of fruits and vegetables on hand to make juice every day. I do consume a lot of fruits and vegetables whole, though, for the pleasure of eating.
I found one of the best things to juice for energy is a bell pepper. Has that sweet, peppery flavor without any heat, and it's about as effective as a cup of coffee for me. Good to juice anyway for the antiinflammatory properties and vitamins. It juices well with sweet fruits, especially lighter juices like you get from melons.
Sometimes I use this book for ideas:
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