You do want to make sure you don't buy into a fund just before capital gains are distributed, because you can be forced to pay taxes on gains you haven't enjoyed. You can find out from the fund company when those gains are distributed. We are discussing mutual funds. Increasing asset size can dilute investment performance. On the other hand, managers with a lot of cash can get in on some good deals.
Large funds can also benefit from economies of scale in terms of the costs of doing business.
If a stock fund hasn't done well in an extended bull market, you might want to reconsider it. What they invest in varies. REITs haven't done particularly well lately, but there is reason to believe they are ripe for a comeback. Forbes magazine also explores other one-bet funds. Those include funds that specialize in utilities, energy, natural resources, precious metals, communications and emerging markets.