I was just wondering, which one is more effective? I haven't done a bench press with barbells, or dumbells in long time because I don't have a spotter. I have been doing the chest press machine at the gym to replace benching.
My max on the Machine was 225 a week ago. I usually do 150lbs for 3 sets of 8-10 reps. I know machines isolate muscles better so would I most likely be able to lift the same weight with a barbell, or is that harder.

I just wanted to know because I want to do whatever works best. Thanks.

What you can do on the machine won't be close to what you'll press with the barbell. Machines work you in 1 plane of resistance, whereas free weights take three. Machines tend to take the stabilizers and synergists out of the equation that are vitally important with free weights.

My advice-start benching both with the barbell and dumbbells. Forget about going to failure and keep 1-2 reps in the hole.

evo...spoken like a true lifter

Also, unless it's a really fancy machine...it's gonna have a straight-line range of motion...when in reality a bench press has a slight arc to the ROM.
Follow Evo's advice.

Thanks for the advice. I think I'll stay away from the machine for a while.
So should I be able to lift more than I did on the machine if I use free weights, or would I be correct if I guessed that it'll be less. I usually work my triceps, and delts with my chest because I knew the machine doesn't target those areas. That'll help with free weights too, right?

Right, free weights incorporate more muscles to a lesser degree simply to stabilize the barbell left to right, front to back, which the pecs, shoulders and triceps work to move it up and down (these are the 3-planes that Evo's talking about).
Because you have a better range of motion you should be able to lift a little more weight...even if it's only 5-10%

In addition to barbell bench press, definitely do plenty of dumbbell bench press, flat/incline and decline. Dumbbells help even out weaknesses you may have between right and left sides of the body, require a little more stabilization...and you can get a little wider ROM as well as squeezing the pecs at the top of the concentric move, like a dumbbell flye.

Also, don't lock the elbows at the top, leave them ever so minutely bent, as this helps keep the stress on the muscles.

So would it be a bad idea to do some Chest Press Machine and then jump on to free weights ?

If anything, do it the other way around. The chest press machine will almost be an isolation machine, so after you've nailed the pecs with free weights, you could hit the machien with less weight and rep to failure. But I wouldn't do that every workout. Maybe every 3rd or 4th chest workout.

i think also personally with the chestpress.. it's harder to apply equal pressure (for symmetry) i notice when i use the chestpress.. my dominent right arm always uses more power then the left.. and it's hard to find the perfect balance in giving pressure when pushing it away... but with the bench press it's easier coz if you dont apply a lot of pressure on the left.. the allignment would be off and you'd see.. that way you'd train both sides equally i think.