i had a t4 2.5 which was superb and towed very well indeed however the loan van i had when my gearbox failled under warranty was a 1.9 tdi 130 and this was a pretty poor, i would not have liked to tow with it. it did have 130 bhp but it really seemed to lack any real pulling power, with this in mind i would definately recomend you get the 2.5. great vans to drive and the sound the 5 cylinder 2.5 makes is addictive, fuel economy was not as good as my transit 2.2 tdci 140 is now but i supose that's the years that make the difference plus my transit is re-mapped to 187 bhp and 10 % better fuel economy.
overall a great van will last and will be a treat to drive solo and towing so long as you avoid the 1.9 tdi.