DD-WRT and Tomato are both old tried-and-true alternatives to vendor firmwares, and they require less tinkering to get into the state that you want, but they both tend to have weird crufty edge cases that never get properly fixed and don't seem to have any clear direction or leadership - they are both a hodgepodge of forks that you have to spend time digging through hundred-page forum threads to find information about. Development schedules are sporadic, and you often end up with dozens of potential builds in varying states of beta and testing which fix this or that but break this or that other thing. When they work, they're great, but my experience with LEDE has been consistently superior than my experience with DD-WRT or Tomato.
Then the dd-wrt folks mentioned that Linksys never actually gave them hardware ... and if I recall, hadn't really been included in the plans to support it at all.
So then I waited and found whenever I looked for the dd-wrt firmware, it always had lots of caveats and known issues.
I gave up. Shelved it and bought a pfsense box for the internet and use a Ubiquity wifi AP.
OpenWRT/LEDE is great assuming your device is well-supported and well-tested. Unfortunately, the wrt1900ac line was never as open as Linksys claimed it was, the LEDE devs didn't get the support they needed from Linksys when they needed it, and so certain things still don't seem to work.
https://lwn.net/Articles/722135/
http://lists.infradead.org/pipermail/lede-adm/2017-November/...
http://lists.infradead.org/pipermail/lede-dev/2017-December/...
LEDE has, in general, active, managed, and unified development. You'd have to hunt down a specific Tomato/DD version that works for you. Sometimes the latest version of DD/Tomato works, sometimes it doesn't. LEDE? Just download the latest stable release, done.
When buying hardware, look at the LEDE hardware support list. Recently I have bought a TL-WDR4300 (get right version) and a Buffalo Airstation N600 router. LEDE runs good on these and the router has enough flash and RAM. Running hardware vendor firmware is not good, IMHO.