I have TD, Fidelity and Vanguard.
What will be you be using the account for? My recommendation would change based on that as well as expected $ portfolio.
If primarily passive investing in low-cost, index mutual funds - go with Vanguard.
If active trading in options, stocks/etfs - TD Ameritrade (software + reporting)
It is easy to do Roth conversions in Fidelity. Full View in Fidelity is good, but there are similar competing prodcuts. Fidelity charges account closing fees. TD also charges closing fees, but waived for Apex customers.
Based on your total assets at the brokerage, you get some other benefits - lower costs, lower fees, free tax software, etc. So best to consolidate as much as possible.