After looking at the "what broker" issue several times in the past, I concluded that if I tried to optimize based on commissions I got one answer, if I tried to optimize based on money market rates I got a different answer, etc. For my particular situation, I finally arrived at a solution that seems to optimize across a number of issues.
I have a checking account at Schwab (in addition to some tax deferred and non-tax deferred investment accounts) that has a free on-line bill pay option and an ATM card that I can use anywhere without an ATM fee (Schwab reimburses my account for ATM charges). I have electronically linked my Schwab checking account (overnight electronic transfers) with Emigrant Bank which has a money market that currently pays me 3.25% on any short-term idle cash. Cash that I can tie up for one year is sent to Corus Bank for their 4+% one-year CD's. Cash that can be tied up for three years is sent to PenFed for their 5% three-year CD's.
A second, large account is held at Vanguard to take advantage of several of their low cost index funds. This account is not yet quite large enough to take advantage of their commission free purchase of Treasury auction offerings, but that is the goal.
All income, expenses and investments are tracked in Quicken, net worth is calculated weekly and linked to the Safe Withdrawal Retire Early Calculator for weekly recalculations, budgets are revised annually and portfolio balncing at 60/40 is done annually. Now that I think about it, I've got to get a life!
Not for everyone, but it works for me (admittedly some of the options require fairly large accounts).