Prefer Sabre, though young horses that won't stand still or are a bit quick with their back legs get Prolites to start with as I lack the patience to do all the buckles up on the Sabre ones whilst the leg in question is flashing round my head!
I got some nice Escadron ones for my girlie last season which are fab and don't move an inch. I bought OH the premier equine vented ones for Christmas and while they've not seen an event yet they behaved for his recent XC schooling session
Another vote for the Escadron ones. They worked very hard last year and we didn't have any problems at all. Easy/quick to fit, secure and comfortable, offer great protection.
Just had to buy a new set though coz ours were kept in a bucket in the trailer and some bug*** nicked it! Grrr!