I find the 'my' form better, for several reasons...
(speed, style...)

But I've seen a lot of experienced programmers using the older form (without my).
(By example, in the Advanced Perl Programming almost all examples don't use 'my')

NOTE : I should add that the speed aspect is only minor,
and this case is one of the (rare) special case where you can use 'my' without making a long code unbearable...
A good discussion on 'my', its danger, its speed gain and optimization could be find here.

"Trying to be a SMART lamer" (thanx to Merlyn ;-)