Its all personal preference really, The fly will be the heaviest and req low pressure bottle. Dont kno the weight of the others. also depends if you prefer a poppit or spool valve marker. Someone else can explain those a bit more as ive only ever had spools.
General rules of thumb:
Poppit:
More efficient
Relatively loud
easy to maintain
Spool:
Not as air efficient
Relatively quiet
Smoother shot
Requires a bit more attention in terms of maintenance
Although the difference between all the high end DM's, ego's and angels will be fairly negligible. The DM will be the least air efficient of the three (only by a bit), but is the quietest. It'll also require slightly more maintenance than the other two, as you'll have to keep it lubed.
(However, keeping a marker in good shape should never be a task that's ignored. It's good practice to look after your stuff, especially if you're dropping hundreds on one. Learn it inside out, and keep it up to scratch.)
The DM is also the only one of all three to not have an OLED display, but you can live without it.
With all this said, though, they're all great markers. It's up to personal preference, so I suggest you try them out, if possible.