If the forces of Númenor and the forces of Gondolin were to meet, which do you think would win? Aside from their mortality, the inhabitants of Númenor had made huge strides in technology. In a passage in the Silmarillion, engines are described as being built by Númenoreans, and in a passage in the Lost Tales, flying machines are also described. These technologies seem to be exclusive to Númenoreans, too. So, technology wise, it seems that Númenor was ahead of Gondolin. However, despite their advanced technology, Númenor didn't make anything that survived into the third age. The palantír of Númenor are speculated to have been forged by Feanor. Narsil, the sword Elendil, a Númenorean, used to cut Sauron's finger off, was forged by Telchar, an elf, etc. Indeed, I can't think of anything made in Númenor, itself, that has lasted into the third age, or that contributed to the performance of some great deed. Gondolin, however, is different. While Gondolin might not be as technologically advanced as Númenor, that which they made was that much mightier. The troll cave that Bilbo and co. found in The Hobbit contained some of the swords of Gondolin, which were later used for some pretty significant deeds. Plus, the Gondolin has Glorfindel, and perhaps others like him.
So anyways, they both of their strengths and weaknesses, but... in the grand scheme of things, who has more strength?
Finally, here's the passage, in the Silmarillion, that describes engines.
Nonetheless for long it seemed to the Númenoreans that they prospered, and if they were not increased in happiness, yet they grew more strong, and their rich men ever richer. For with the aid and counsel of Sauron they multiplied then: possessions, and they devised engines, and they built ever greater ships. And they sailed now with power and armoury to Middle-earth, and they came no longer as bringers of gifts, nor even as rulers, but as fierce men of war.
and here's the passage in the Lost Tales describing their flying machines:
'And behold what hath happened since, step by step, At first he revealed only secrets of craft, and taught the making of many things powerful and wonderful; and they seemed good. Our ships go now without the wind, and many are made of metal that sheareth hidden rocks, and they sink not in calm or storm; but they are no longer fair to look upon. Our towers grow ever stronger and climb ever higher, but beauty they leave behind upon earth. We who have no foes are embattled with impregnable fortresses - and mostly on the West. Our arms are multiplied as if for an agelong war, and men are ceasing to give love or care to the making of other things for use or delight. But our shields are impenetrable, our swords cannot be withstood, our darts are like thunder and pass over leagues unerring. Where are our enemies? We have begun to slay one another. For Númenor now seems narrow, that was so large. Men covet, therefore, the lands that other families have long possessed. They fret as men in chains.
