When testing I prefer to do it in person whenever possible.
If the design is still on paper I use A4 or A3 printouts, paper cutouts, sharpies, highlighters, sticky notes and a faux-pointer/cursor (or finger). This is easy, cheap and hands on - important for getting to grips with my work before I get distracted by the limitations of working digitally.
If sketches or designs have been captured for mobile testing I usually use Marvel because it works smoothly, is maintained by the developers and is free. (Although I see my older favourite POP is pulling it's socks up again after being bought out by Marvel back in November). POP used to have issues crashing after loading new screens, and the interface had been designed assuming all users had newer/larger mobile screens (I didn't) so chopping off controls at the bottom of the screen. If I need to record the user's fingers offscreen too, I use my IPEVO ZiggyHD document camera on a desk.
For larger screen testing on my laptop I use Silverback to record the screen and a video of the user's face simultaneously. Silverback is built by the Clearleft team and was one of the first apps I used that integrated recording the screen with the facial emotions of participants. I've never found a reason to stop using it and it only costs about $40.
I use Optimal Workshop's OptimalSort for online card-sorting. It does exactly what I need it to, is flexible, and gives me great reports for analysis. Likewise, I use their Treejack for testing information architecture.
For simple remote navigation or click testing I like to use UsabilityHub. In addition to the team being personal friends who live around the corner, the tool is simple and effective and the pricing tiers flexible when I need them. In the past I've used others, including UsabilityTools, UserZoom, and Loop11.