I haven't seen a Tuscan boiler but their claim to uniquely offer a balanced flue external model simply isn't true. And hasn't been for years.
The Worcester Camray condenser, I'm assuming you are referring to the 2005-2013 model as the Mk1, wasn't a disaster. It wasn't very quick to service which might be a pita for the service tech in a hurry, but an 8yr lifespan of production, with very few updates (just baffles and a better condense trap as far as I recall) shows it was well up to the job. The many we have fitted are all still going strong.
Grant do not have a blemish free record, as anyone with a contemporary Vortex combi will tell you. The electronics were rubbish, the water tank splits if the expansion vessel loses charge and then writes off the whole boiler, their vertical flue termination leaks on the top hat connection and the condense trap is lousy compared to ...a Worcester.
Took out (eg: scrapped) a 5yr old one last month with a split water jacket due to the exp vessel.
Their warranty is administered by (usually) cheap subbies and it isn't 7 yrs like the Worcester, who have their own dedicated tech team on the road.
Grant aren't a bad boiler, but I just wanted to redress the balance and show they aren't perfect.