Yeah, you're stuck with the 401k. Don't forget about IRAs, too.
wrt your original question, I'd put new money into Vanguard. Moving the old money depends on how much in capital gains taxes you're going to have to pay and how long you plan on leaving it in there.
I map scenarios like this out in Excel. For example, say you had $10k in TIAA-Cref with $1k of that gains that you'd be taxed 15% on if you took it out. Moving it would mean you'd only be depositing $9150 in Vanguard (10000-(1000*0.85)), so if you assume you get the same market returns in both funds Vanguard will take some time to catch back up. It would take 11 years in my scenario (using the .98% ER vs. VTSAX's .05% ER, with a 7% rate of return). That's a long time, but MMM is fond of pointing out that 10 years should be your *minimum* time horizon for making these sorts of decisions. After 30 years the difference is $68k in Vanguard vs. $57k in TIAA-Cref - the effect magnifies at longer horizons.