There aren't best methods really, it's only up to you to decide what you need. Internal devices mainly offer comfort and faster rehabilitation, while externals offer less-traumatic surgeries with less long-term complications, less surgeries, much cheaper costs and full weight bearing regardless of your weight. Say, you want to lengthen your tibias by 5 cm, here's how it looks like with both methods:
Internal: you'll be lengthening 2 months, the lengthening phase isn't much different from externals, as you'll severely limited in your movements. After another month or two, depending on your consolidation, you should be able to walk unaided and normal. So you can say the full recovery time with internals for 5 cm is 3-4 months. You'll want to remove the rods later on, but still.
External: you'll be lengthening 2 months, and you'll need another 3-4 months before you can remove the external device. So that's 5-6 months for 5 cm. Also keep in mind that while in externals even after the distraction phase you're still limited in your movement, clothings.
I guess it'll be fair to say that the overall rehabilition time is twice as long with externals. Like for 7.5 cm internally you'll need 5-6 months to start walking normally and with externals it'll be 10-11 months.