Personally, I just have two routers....
I've thought about dual-WAN, but without rewiring my apartment...don't see an easy way to bring the two together.
So, in the livingroom, where the only cable outlet is....I have cable modem (and other stuff...like 2 TiVo HDs and a TiVo Premiere...are connected) and a router. And, then at the other end of the apartment where the telco box is....I have DSL modem and another router.
I had originally gotten the extra router on impulse and as a backup....digging around at a Walmart I had found a WRT54GS ver 1.1....so I'd have a backup in case I bricked the WRT54GS ver 1.0 router. (as it happened I bricked the ver 1.1 router a couple weeks ago, but I was able to reset to factory and then mostly recover....it has been over 2 years since I backed up the config
Anyways...both routers are in use.
They are setup as different gateways on the same LAN.
Most of my computers are pointed to the cable modem gateway by default...the Linux boxes know how to talk to the DSL gateway (as well), so I can have some apps on them talk that way....I have squid proxy running on one...as one way to go between the two gateways easier.
Other devices in my home are set to use one or the other gateway.
I can switch things between gateways as needed....some easily, some not.
For me...cable is the faster link (usually), but less reliable. And, DSL is the reliable one (usually)...though not as fast. My VoIP ATA is usually pointed out DSL. The TiVo's are usually on cable, so I can netflix stream....
Most of the wireless devices use DSL, because when a storm knocks things out...cable usually goes out and stays out longer than the power does. But, I have hefty UPSs on the network equipment....especially on the DSL + VoIP end....
So far in my time....I've only had two DSL outages. One, a box somewhere took damage and everybody was (DSL) dark for rest of the weekend...the other time...somehow the storm caused my DSL modem to lose its mind (had to re-enter my login/password). ... yes, I use PPPOE on the modem.
In the beginning, I could only get 1.5/256 DSL....but now I have 6.0/768. But, cable is at 12/1.5 (upto 15/2)....though not sure I'd get that with all the students in town now....
It all works well enough.
You may be a dreamer, but I'm The Dreamer, the definite article you might say!