I am quite content with my Dyson DC24 vacuum. But while I love that it's fit for all floor types, it doesn't lose suction, and it's easy to move around, if I were shopping for another vacuum, I'd really only have one priority: power. A powerful motor makes for a powerful vacuum. So when you're shopping for your next cleaner, remember that its strength is in direct proportion to how much dirt it will lift as you pass it across your carpet. Pick the one with the highest strength!
A 12-amp motor is fairly standard, and anything less than that won't be very productive. Meanwhile, a vacuum with more than 12 amps will send more power from the outlet to your motor.
After you've found a few selections with a good strength, suction power (mine is 220 AW) will be next important, and then you'll want to narrow down other needs like floor types and size.