i have personally never had any problems with the square taper interface on cranks, i use middleburns with a hope titanium bottom bracket, but then again im not very heavy, i have never rounded an interface, square taper on my middleburns but have on older model cranks,
isis is o.k. but i have never had the need to move to isis, if i did then i would probably buy the tensiles, they are great value for money, well machined and the looks are great.
regards ash