There are a lot of alternative layouts out there, all of which are roughly similar in terms of calculated efficiency (and all a good deal better than QWERTY).
BUT, they differ in terms of what they are optimised for. Dvorak and Colemak are currently the most popular for various reasons. Here is a brief analysis of both:
Dvorak:
1. Old layout, designed before computer analysis.
2. Designed for hand and finger alternation when typing English as opposed to finger "rolls".
3. Has all the vowels on the left hand home keys.
4. Has the most common characters on the home row (U is an exception).
5. Spreads the load evenly between fingers.
6. Doesn't keep shortcut keys in the same positions as QWERTY and is very different in general from QWERTY.
Colemak:
1. New design, analysed by computer for maximum efficiency in terms of finger distance.
2. Designed for inward "rolls" of the fingers when typing English words.
3. Has most of the vowels on the home row.
4. Has the most common characters on the home row (with U positioned more in line with it's frequency of use).
5. Loads the index fingers more than the others.
6. Keeps ZXCV in the same position as QWERTY and has more similarities to QWERTY.
Personal issues with each layout (please note that though I point out facts about each layout, how each affects the typist is personal):
Dvorak:
1. Letters "U" and "L" are in awkward positions.
2. Overloads the pinkies, but not too badly.
Colemak:
1. The factors used in the analysis don't suit how I type. Finger travel distance is not the most important factor in typing efficiency, IMHO.
2. Inward finger rolls don't suit me, although they probably do suit most others. I find outward rolls more comfortable. I find alternation even better, though.
3. Overloads the index fingers. I prefer a more even distribution, although with less load on the pinkies than Dvorak.
4. TOO similar to QWERTY. I prefer a layout to be very different, so I can learn it without affecting my QWERTY skills during the learning period. This is important if you use a keyboard for your work. Similarity can create confusion in your muscle memory during the transition and even afterwards. You may be required to use QWERTY layout now and then after you have learnt your new layout.
So, it's up to you to decide what factors are more important for you and learn whichever layout matches best. Personally, I put off learning a new layout until I got my DIY keyboard made, since the physical layout is even worse than the character layout in terms of ergonomics, but that's another story.
So, I went for a layout optimised for my new physical layout and the factors that matter to me, AdNW BU-Teck modified for English only. It focuses on alternation, common chars on home row, short finger travel, modern analysis with different weighting on each finger, etc. Optimised for keyboards with staggered vertical columns (instead of horizontal) and thumb keys clusters. Here is a heatmap for it with "Gulliver's travels" as a source: