Here are the cubes I use. Take a gander.
2x2 - Maru - lubed with Maru Lube. My first decent 2x2. The corner cutting is phenomenal and overall I really enjoy this cube.
3x3 - GuHong (black with colored core) - lubed with Maru Lube. Excellent 3x3. It's a little smooth for my liking; I prefer a cube with a slight clicky feeling but this will do. I also enjoy my Maru 3x3 Old Type DIY. It's nice.
4x4 - Yeah...*cough. I use an Eastsheen. Clearly I don't care about 4x4 too much. Actually...I'm about to get a new one. Leave a comment below saying which one you think is best.
5x5 - Modded V Cube 5 - Lubed with Kel Silicone Spray - The mod definitely helped. At first, it just felt smoother, but the cube was still extremely tight. After lubricating it and solving it 20 more times the cube got better each successive solve. Highly recommend rounding the corners.
6x6 - Modded V Cube 6 - Lubed with a liberal amount of Kel Silicone Spray - The mods were unintentional. At first, I just wanted to stop the clicking. However, after sanding everything down, I realized I was committing myself to do the pin mod as well (insert facepalm emoticon here). So...I did. Luckily, it only took 30 minutes for all four pins. Super easy to do. Great cube.
7x7 - Regular V Cube 7 - Not lubed...yeah, I don't care much about 7x7.
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Thanks for reading,