"Smart routing" is a term tossed about by brokers who do not understand how things work.
Many firms and ECNs just use a step by step order routing.
e.g. first matches in house book, then routs to ECNs with Direct Links established, then uses Nasdaq services.
This is how ARCA works since you mentioned them.
The absolute most abusinve use of the term "smart" is when all of your orders are sent to one place like ARCA, and your broker just piggy backs ARCAs "smart" software. There is nothing wrong with piggy-backing ARCA, it is effective. But, it is wrong to claim you have "smart" software.
Sometimes brokers hide their inadequate "smart-ness" by using the term "proprietary algorithm." If you hear this term you know they do not have any "smart" software at all. It likely routes to one ECN or market making firm.
There are some firms that do design in some "smart" software. But from what I hear from programmers, it is very time consuming to do a lot of market analysis before sending an order. This of course will result in slow executions. So "smart" (in my opinion) is not bad nor good, just a term thrown about by marketing people to get new accounts.
What is truly important is the ability to know where your orders are going, and what type of routing is provided. The more access and direct lines your broker has to exchanges and ECNs, the more able you will be to trade will all quoting participants.
In the end... ask yourself... who's quote do I see and can I get to it effectively?
