Another 'custom looper' here mate. Kougar is spot on the money with regards to water vaporisation and galvanic corrosion. Won't be an issue if you're expecting a service life of just the warranty period, but they all dry up eventually.
What's the budget?
The bigger names in watercooling (XSPC, EKWB, Koolance) offer a huge range of kits at usually stupid prices, but of particular note is EK's latest release - the FluidGaming kits. This is EK's first real go at mainstream OLC kits, and it's worth a look if budget permits. It's Aluminium-based, so you'd not want to mix it with 'regular' EK blocks (mostly copper) or other manufacturers' gear, but they'll sell you a kit with a 240mm radiator, CPU block, reservoir/pump combo, fittings and tube
pretty cheap. They even offer
GPU blocks in the same family so you don't have to mix metals. There's
expansion packs with more radiator, as well.
If you stuck to FluidGaming products and used a corrosion inhibitor in your coolant, it seems like a solid option, especially if GPU temps are a consideration. You're getting a decent pump, a reservoir you can top up, the ability to cut your tubes to whatever length you need/want, and some appropriate coolant. I wouldn't normally point you in the direction of Aluminium for custom loops (and I'm not alone), but EK seem to have 'done it right' and you can build just as good a loop out of Aluminium as you can out of Copper now - it's a pretty big deal and I've been doing a lot of reading and giving it a lot of consideration myself. You
will lose the 'all-in-one' monitoring convenience of a CLC, though.
if you're the sort of person who transfers gear over between builds and doesn't necessarily have to have brand-new-everything each time you update, there's merit in taking the custom approach, even compensating for my bias -
if the budget permits. It's gear you just keep bringing forward with you - you only swap blocks as you swap sockets, and you top your fluid up once a year, tear-down and clean your blocks every two years or so - that's it. Oh, and you save 30C+ on the CPU and GPU load temps. It's also nowhere near as hard as it was back when we used garden hose and custom blocks of copper and stuff - if you can put fittings on a garden hose, you can set up a custom (soft-tube) loop.