Either way as others have pointed out lump or DCA it all works out in the end. There are examples where Lump>DCA and there are examples where DCA>Lump. I think DCA will win at the present time.
If you honestly believe the market will probably go up this year, the best thing to do is to contribute as soon as possible. If you honestly believe the market will probably go down, the best thing to do is to save up until the end of the year before investing at all.
Spreading your purchases out (when you have the cash available to invest in a lump sum) is never the best thing. If you do this you're just hedging your bets, saying you don't know whether the market will go up or down, you believe each outcome to be equally likely, so you may as well spread it out a bit so that you don't get unlucky and put all of your money in at the low point.
The flaw in this logic is that rising and falling are
not equally likely! In any given year, either one can happen, and neither one should be a big surprise. However the reason we invest at all is because we honestly expect our investments to go up more often than not. Invest each year as soon as possible. Compared to delaying your contributions until later in the year, you'll win some years and you'll lose some years. However the probability of losing more years than winning over the course of your investing lifetime is extremely remote. So if you have a crystal ball that can tell you that this year really is going to be a losing year with any certainty, go ahead and use it. If not, trust that time in market beats timing the market most of the time and quit worrying about short-term movements.