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I suppose it depends on the passenger - much like how some people only think of cars in terms of 'blue car and red car' vs BMW, Audi, etc, some people just don't think of things like that as being important. And with the many different types of train, it's difficult to speak generally. But - a diesel-powered train has to carry its own fuel supply, which an electric train doesn't, so the difference in weight means an electric train will probably be faster to accelerate than a comparable diesel-powered train. I've heard of some people complaining about the hum & vibration of diesel engines underneath the floor in a multiple unit, but I think they are just fussy. And, I guess it's nicer for people who live near train tracks if the rolling stock is electric rather than diesel, due to the diesel exhaust and engine noise.
Personally, I think it matters more to passengers whether their train is formed of multiple units, or unpowered carriages hauled by a locomotive. Both have their inherent advantages and disadvantages, but they're different advs. and disadvs. from a passenger's perspective - for example, because of the way the engines and powered wheels are distributed through the train underneath the floors, a multiple unit will probably be faster to accelerate than a locomotive-hauled train. Likewise, I don't think double-decker multiple-unit trains exist, due to the space needed by both the underfloor engines and two passenger levels. (and then you run into the different methods of adding capacity to a line - the German/British 'long trains' vs the French 'double-deck TGV')
