It was a hypothetical question, if you have to have one lens only what would it be, in reality if course few of us have to make that choice and have lenses that are favorites for different reasons.

There are lots of good third party lenses, of the three popular brands Sigma, Tameron and Tokina, I have only uses Sigma and Tameron, of those two sigma are for me the clear winners, I have always found the Tameron softer like for like to the point that I returned one  twice, and in the end gave up and got a refund, personally I would never get another.

The cheapest lenses are never likely to yield great results, but most of the mid range lenses are very good.

I don’t  agree that if you are only doing web images that lesser quality lenses are sufficient, even at that size poor optics are noticeable.

If you are shooting portraits you really need the eyes to be sharp or they just don’t work, that is exactly where the primes really show their worth.

They wouldn’t have made the cane if you weren’t meant to break the rules