Photographers what do you think of Tamron and Sigma lenses?

Like all equipment there are good and bad. Even different lenses from the same company can be hit or miss. My daughter is using a Sigma lens I gave her (28-200) that's about 15yrs old. Works like a champ. I have a Tameron 28-300 that had a 4.5 star review and it has better color than some of my primes. I would look at reviews from like DPReview and see what they say about the lens you are looking at. When I bought mine I saw lots of 3.5 and 4 star lenses from Tameron but mine was found to be exceptional. Good luck!