I currently have several products from both Logitech (1 wheel, 1 joystick, 2 mice, 3 keyboards) and Razer (1 mouse, 3 keyboards, 1 game pad) that get very heavy usage. Plus I've had older products in the past. Both have pro's and cons.
Razer's software/firmware goes in spurts. Their more "basic" products have far less issues. It doesn't seem to be Synapse itself (which has gotten much better and I actually like the cloud portion) as all their products use the same application and I only have issues with certain products. For example I've had ZERO issues with my Razer Naga with probably a thousand hours of usage on it. I mostly use the side buttons as a plain numpad, but I've done macro's too. They've always worked fine. My Deathstalker on the other hand has been flakey since day one. No mechanical issues. Key's will randomly soft "stick" meaning fail to send a release command until you press something else. This includes the touchpad. The touchpad only loads it's wallpaper maybe 75% of the time. The backlighting has forgotten it's color settings a couple of times. But those are just annoyances. Annoyances you shouldn't have to deal with on a premium priced product, but annoyances none the less.
My Logitech's on the other hand.... While I think their software is a bit outdated and bloated, I've had little to no issues with it. I've done a pretty substancial amount of macro setups on my G13 and it's worked flawlessly. Some of their older products require an older version of their software which doesn't work with their newer products. However the finish on every backlit Logitech product I have owned has worn off 10x faster than any of my Razer products (faster than my Saitek Eclipse too). I consider that more than an annoyance. The finish across the board on my Razer products looks and feels better than the Logitech products IMO.
Products currently used:
Logitech - K810, diNovo Mini, G27, 2x G5, G13, Extreme 3D Pro
Razer - Deathstalker Ultimate, Naga, 2x Lycosa, Onza TE