I have had a pair of the newer Simms G3 felt bottom boots for about a year now. I find them comfortable and have been holding up very, very well so far. My only complain is the laces that came with them were junk and shredded the casing in a few trips. I put on a different pair of thicker simms replacement laces and they have help up good so far.
My previous pair of boots were older Simms Freestones and they definitely felt heavy but I couldn't believe how undestructible they were through the abuse I put them through. They are still a solid pair of backups for me.
I used to wear another brand of boots, because I really liked the interchangeable soles, but three out of the four pairs I had were falling apart in less than a year.