They're different in effects. Many will produce a mind racing high not the couch lock sit on the couch baked type of high. That effect is not desirable to many. Especially those that already have a high level of anxiety.
Many don't allow them to fully finish flowering and harvest early which can lead to an underwhelming high. They also don't take well to the high EC feeding many use and end up struggling with unhealthy plants from overfeeding. Also the drying process can go much quicker as the flowers are typically not as dense as indicas and hybrids which can lead to flowers drying too quickly and being over dried which results in a poor quality end product.
As far as sativa genetics go ACE is the place. I've grown quite a bit of their stuff and all of it has been great. I have some of their Malawi flowering right now and have a few more of their strains that I haven't grown yet but am looking forward to.