It's a nice choice to have. Williams is going to help more right away. He should be an ok WR3 this year - maybe 60/800/6 type of season. He's a very natural receiver, on par with Dez as far as being able to come right in and play. I think Thomas' upside (and risk) is higher. Thomas is a lot more raw in his route running, but his size/speed combo is a lot more freakish if he puts it all together. Thomas could be top 8. Williams could be top 15. A lot of rosters I would rather gamble on Thomas. But you have to be committed to a 3 year plan and not cut bait like some Sid Rice owners did.
I've read a lot of negatives about Thomas, specifically that he lacks speed
This part is wrong. He ran a 4.38 40 at his pro day. He is faster than Mike Williams (4.49 at combine).