An SMS route is the path a message takes from the gateway to the destination operator, through a given carrier or aggregator connection; routes differ in delivery rate, sender fidelity, receipts and price.
For any destination a gateway can usually choose among several connections. A route is defined by who terminates the traffic and on what terms: a direct operator connection, a national aggregator, an international wholesaler. Each has a measurable delivery rate, a latency, a way of handling sender IDs and receipts, and a wholesale price.
Providers that sell "premium" and "standard" tiers are selling two routes at two prices. A provider with one route per destination has chosen for you, and the question is on what basis.
At SMSMeteor: one route per destination, chosen on measured delivery rate and reviewed daily; the published rate does not change mid-campaign when the route does.