Microtex is a thinner, sharper needle. It makes the smallest hole in the fabric of any needle. The eye is smaller. I love them for all piecing & most quilting (for vintage/repro fabrics, I prefer a Quilting needle), but I have no problems threading my needle or changing needle type to do garment construction & home dec.
Topstitch needles were originally designed for topstitching heavy fabrics like jeans, upholstery & handbags. The industry then found they're great for all commercial sewing applications because you can go from one item to the next, from quilting to sewing jeans to working with vinyl or leather & the Topstitch needle will sew through them all. But I think of it like using a 7" chef's knife to stem & slice strawberries. Yeah, it'll work, but the results won't be as pretty as if you switched to a pairing knife. That said, if you're on a budget or if seconds matter to your schedule, Topstitch is the way to go. Likewise, if you just can't get your needles threaded, Topstitch will make things easier for you.
Also, I would switch to a size 80 Microtex for 50wt thread (70 for some brands). 90 Microtex partially defeats the purpose of the thinner needle design.
Good luck & happy quilting!