This depends on your type of pallets.
Are they open or closed base or a mix of the two? (See pictures below). Open base pallets include 800 x 1200mm “EuroPallets” and closed base pallets include 1000 x 1200mm BS or Chep pallets. Closed base pallets can also be 1200mm square.
Narrow straddle leg stackers are designed for use with open base pallets. Wide straddle leg stackers are for use with both open and closed base pallets.
To explain how pallet type affects your choice consider the model on the right. It has narrow straddle legs which makes it very manoeuvrable. However, the narrow legs prevent it from lowering closed base pallets to the floor. You can see it will actually place such a pallet on to its own straddle legs.
To overcome this problem the closed base pallet can either be lowered on to wooden blocks slightly higher than the straddle legs or alternatively be placed directly onto an empty open base pallet. It seems that most customers prefer narrow straddle stackers for their manoeuvrability and accept this compromise.
The stacker on the left has wide straddle legs and will handle both closed and open base pallets right down to floor level. Furthermore, because of its extra width it is extremely stable, particularly at height, and its larger wheels cope better with floor irregularities. However, it is much larger to manouevre and spaces must be left between adjacent stored pallets to accommodate the width of the legs.