It depends on my gig, in the wedding band I always use my own amp, but in the original band it really depends. I almost always bring my own head, or small combo to a gig, but often for short gigs with a few bands I use the house gear or one ore the other bands stuff. Sometimes I let other bands use my gear, but it depends on the band. I need my gear to be working or I can't play wedding gigs, and they pay the bills.
I've only played one venue who wouldn't let me use my own rig, initially when I heard this I was a bit confused, but once I arrived I understood. The Moorings bar in Aberdeen has a great in house setup, an ampeg, a Marshall and some other nice guitar amp and drum kit. It's all on stage in position to get the most out of the space and save time setting up. Because of that and an engineer who knew what he was doing, it was my favourite small(ish) venue I've ever played.