I've likely posted much of this before, but...
There's no difference between the performance potential of Weber DCOE and Dellorto DHLA carbs once setup properly; however, they're not simply clones of each other. There are very distinct differences between them. And there is a huge difference in getting them properly setup.
Webers were initially designed for Racing, where the carb spent most of it's time at WOT. Early italian manufacturers such as Alfa Romeo and FIAT had difficulty adapting them to their street cars. Dellorto came along and used the excellent Weber design, but perfected it for street use. Both of these carbs are now close to 100 years old.
Personally, I prefer Dellortos. But, I'm not trying to be contraversial here - if you like Webers, use them.
One of the reasons for my preference is Dellorto calibrated parts, like jets and mixture screws, offer much finer resolution - you can be more exact in adapting them to a particular engine.
Weber Main Jets are available in size steps of five - 130, 135, 140...etc.
Dellorto's are available in steps of one - 131, 132, 133, 134...etc. Same with Idle Jets, Accelerator Pump Jets, etc...
The Weber Idle Mixture Screws have blunt tapers and coarse threads, while Dellorto's have long slender needles and fine threads. Weber mixture screws usually end up adjusted about 1 1/4 - 2 1/4 turns out, while Dellorto screws end up 2 3/4 - 3 3/4 turns out.
Overall, it's much easier to achieve a very exact mixture setting with Dellortos, while you must take larger steps with Webers that just sort of get you in the neighborhood.
For tuning, the Dellorto is ported to accept a 4-pot manometer such as the Morgan CarbTune II. With this, you can dial in the carbs within 99% in under 10 min., all the while keeping the air filters in place and accounting for them. The Webers rely on an airflow meter, such as the Carb Sync which literally sits between the intake air to the carb and can disupt the very thing you're trying to gauge, plus it doesn't take the airfilter into account.
The Weber progression circuit often has only 2 or 3 holes, while Dellortos have 5 or 6. The Dellorto 6-hole progression is a Lotus development for their own models. Because it worked so much better, Dellorto later adopted this across their full product line.
The 6-hole setup gives the Dellorto a much smoother progression off-idle so the carbs depend less upon a heavy shot from the accelerator pump.
The Weber uses a big pump shot. So much so that Weber carbed engines often deliver significantly shorter piston ring life compared to Dellortos because the big shot from the Weber washes the oil from the cylinder walls.
The Weber accelerator pump's piston runs in a bore machined into the body. It's metal to metal, is subject to "blow-by" due to clearances, tends to wear over time, and the bore cannot be repaired.
The Dellorto diaphragm pump has no blow-by and clearances don't wear with use. Then when it does get old, the pump is easily rebuildable back to 100% spec by simply replacing the diaphragm and gasket.
Webers are much more prone to leak. Dellortos don't. In fact, Lotus switched from webers to dellortos specifically to correct fuel leakage issues.
So, while more difficult to find, and with a more limited number of parts suppliers vs. Webers, I'd still take Dellorto DHLAs over a set of Weber DCOEs any day for the reasons stated. But, having said that, they are both great carbs.
Cheers!