What is the diameter of the largest bar you have to put through the spindle?
What is the (swing) diameter of the largest casting you have to machine, similarly what is the largest diameter of flange or chunk of round bar you have to machine?
What is the maximum length you have to machine between centers?
How much money do you have?
You should be able to make a decision based on the answers to these questions.
I have two SL10s, two HL1s which are similar to the SL20 and two GT20s, they each deal with different sized jobs. Working within their capacities they are all equivalent in terms of initial cost versus productivity.