For a basically stock engine it is difficult to beat the dual SUs.
Why?

Well... for one, Volvo did all the heavy lifting in figuring out how to get them to effectively and efficiently work. Several needle combinations are available for differeing engine configurations and are well tested.
Second, they are dead simple. As mentioned, getting the throttle shafts leak free is a key but apart from that, there is little to go wrong and adjustment for differing elevations, heat/density, economy/power, is all a matter of a little twist of one nut each.
In fact, the SU is still manufactured by Burlen Fuel Systems of England so entire new carbs as well as any part you desire are still available NEW. They are also improving the systems. As an example, the new throttle shafts are teflon lined steel inserts so you will never need to rebush a carb body again (just replace shafts from time to time).
I challenge anyone to get a decent Weber set-up in place for less than fixing your SUs.

OTOH, some people like to mess with boxes of primary jets, secondary jets, air correction jets and emulsion tubes. Then keeping the various passages clean and getting the enrichment pump and nozzle just right is good fun too. Leaving one all winter with old gas is a blast too as getting the gum out of all those little passages (oops don't lose those check balls!) is a hoot.

Then you get to attempt to tune it to your engine at your elevation for your specific air-density (on that day) for optimum performance so you can go and do it again next week when it is 10 degrees warmer (or cooler) or you go to the mountains, or whatever.

Um, yeah, then getting the fuel condense in the intake manifold and alternately flooding and starving the engine is so much joy I can't wait to do it to my car all over again!

Just my (been there) 2 cents worth.

--
Mike!