Software load balancing solutions have now more algorithms such as least time (nginx+ for example).
And yes some ISP cache DNS entries for a long time... But DNS load balancing should be used only on disaster scenarios to mitigate.
The vast majority of ISP caches won't keep your low TTL records in cache for years, but some do; this is a problem if you have to move your load balancers ever too though.
Depends on how stable your servers are vs your load balancers, and how many connections you need; and if you have enough IP addresses to give public IPs to your servers. Also, if you really absolutely need to control the load precisely, DNS isn't going to ever give you that.