One thing we must understand is - both these cars are meant for the rural market. In that market, their priorities are ruggedness, ease of maintenance and reliability. They dont care about ergonomics or leg room.
While I am scouting for used Sumos and Boleros, my personal preference is a Sumo because it has more space. But more than anything else, I am preferring a Sumo over a Bolero because it is available for cheaper in the used car market when compared to a Bolero.
For example, the asking price of say a Sumo which is a 2008 model and has done 65-75k is something like 3-3.25 Lacs. A Bolero of a similar condition asks for 4.5-5 Lacs. Thats a cool 1.5 Lacs more and trust me, there are buyers out there who are willing to pay and premium and still buy an older Bolero over a Sumo. Dealers wont even negotiate much on the Bolero, again because there is a huge market for used Boleros.
Now, there is a reason to this -
1) I am looking for a rugged vehicle to be used in construction sites. People who have worked in those conditions for many years and have operated vehicles there suggested me that I should look only at the Bolero. Sumos are reliable but do tend to develop mechanical issues more than the Bolero. They say "A Bolero (especially the DI) is a fill it and forget it vehicle". When I say ruggedness, please note I am not talking about usage on rough roads. This is usage on no roads and very dusty and harsh conditions.
2) They say that even if I pay a premium for the Bolero now, it will eventually be more economical as the Bolero gives better FE, has cheaper spares, is easily serviceable, is comparatively more reliable and also has better resale value.
That said, I will still be buying a Sumo for the site as my budget is low and in that budget, if I look for a Bolero, I will have to buy a 2005-2006 model which has done about 1.5 Lac kms! On the contrary, in the same price, I will get a 2008-2009 Sumo which has done about 60k-80k.
I recently wanted to buy a Sumo Grande but a cousin who has a workshop in Nashik asked me to stay away from it saying that it has engine and suspension issues. He asked me to prefer a Bolero DI, Bolero m2Dicr, Sumo Gold or Sumo Victa DI in that order.