What bobcatguy said is pretty much correct. The big difference is a 330 is the old K series vs a 630 is an M series. The cab on a K series is a Chevy, the M is a Cadillac if your looking at a full cab. GPM is basically the same, unless you are looking at a high flow then the 330 has about five more. Relief pressure is 3300 on a 330, 3500 on 630, big whoop. Both could run any attachment, except a tree spade, a 630 is a little too small to be serious. The arm design differs greatly. A 330 is vertical vs a 630 is radial. Both styles offer advantages. One thing to add, all 330 are 2 speed vs an option on a 630. I'd say it comes down how much you need to lift and if the reach at max height a vertical lift offers is important. Personally, I like radial lifts and would take a 630 over a 330 unless I truly needed a 330 capabilities. A 330 is replaced by the 770. The 850 is its own monster, more on the physical size of a 963. All that said, if the choice was a 330 vs a 770 with a interim tier 4 engine, I'd take a 330. The new engine is garbage.