It's not easy to say which is "better", but they will definitely be different.
First, if you go straight from a tube head to the PA, you'll need some way to match the output of the head to one of the PA's inputs, and you'll want to simulate the sound of a guitar speaker cabinet. A good way to do this for a tube head is with a speaker simulator and a passive load box. The speaker simulator shapes the speaker output sound from the head so that it sounds like it has been run through a speaker cabinet and miked up, and most speaker simulators have an XLR output which is good for running to the PA. The passive load box is to provide the correct amount of resistance to the tube power output. Without that, the head can easily supply too much current which can damage the head.
Advantages of Speaker Sim with Load Box:
- Reduced stage noise
- Consistent sound
- Light weight (no cabinet to carry!)
- Less expensive than some cabinets
- No mic bleed
Disadvantages of Speaker Sim with Load Box:
- Power supply or phantom power usually needed for speaker sim
- The sound is not quite authentic
- Good monitoring must be available to hear what you're playing
- "Good" guitar feedback may be more difficult or impossible to get
- Ground loops are possible
- Mix/Monitor engineers may not like the setup as much as their favorite mic in front of a cab
- You'll need some kind of monitoring setup for band practice, which will likely sound different from the live shows
Obviously, the advantages and disadvantages of going with a miked speaker cabinet are pretty much those two lists reversed. Personally, I prefer either a small head and cabinet or a combo amp. I make it so the amp is pointed at my ears, instead of my knees, so that I'm getting the loudest and most direct guitar sound. I set up the same way at practice as I do at gigs so I can keep my sound and feel consistent and also play with feedback in a more consistent way. Using a smaller, lower powered amp helps with reduced stage volume and bleed into vocal mics, saves my back (smaller amps are lighter), and makes sound engineers happier.
I do own two great speaker sims and two different kinds of load boxes, but I just can't handle the difference in sound and feel. I use them mainly for doing scratch takes when recording or for playing along with a drummer when laying down drum tracks, so there's no guitar bleed into the drum mikes.
As a sound engineer, I usually actually prefer to mike up sources, rather than DI. I do bring a lot of DIs to a gig but I don't bring speaker sims. A guitarist rolling with their own speaker sim would be a pain, IMHO, since it would be directly connecting gear that I have no expectation of function or reliability. With a mic, you know there are no ground loops and you know what the mic is going to give you, because it's your mic. It's almost the same with a good DI, although a lot of direct sources require a lot more processing (compression and EQ) than miked sources.