The 150 is no more than a siphon fed 100. Same head, needle, air valve, handle etc. Only the main body is different. Being able to put a large container or a small color cup is very handy and the sight line down the 150 is superior to the 100LG, as it doesn't have a huge cup on top. Some people prefer the 100G for that very reason.
The 100 series is a gravity fed AB and therefore requires slighty less air pressure to atomize the paints, thereby it can do slightly finer details. Actually, it's not that it can do finer lines, it does them with less overspray, so the control is better. It also uses less paint as it doesn't have a siphon that requires additional paint. OTOH I find the 150 easier to clean, as the cups or bottles can be dealt with seperately. It's a tough decision, and one that I overcame by buying both!
It all comes down to what you need. If all you need is good solid coverage, with the occasional need for pencil thin lines, the 150 will be fine. If smoke ring camo is your thing, the 100G or LG might be a better choice.
In fact the Crescendo can do much the same as the 150, but it's more of a fire hose. You have to be careful not to "open it up" as you'll be amazed at the amount of paint it can put out!!