First, there is no "best". Everyone has different needs and ears (after all.. you play what sounds good to YOU not someone else).

For me and the way I play it is Tubes, 6V6 or 6L6 and fairly small wattage (less than 35 watts).
Modelers have come a LONG way in recent years but, seems to me, they haven't quite got the touch response and attack down yet. Maybe someday.

Tubes - Mesa Boogie Dual Rectifier Solo head -
I like the sound of real tubes and modellers haven't got it right. Most non-tube amps try to advertise that they aren't tube amps but sound just like thiem. I disagree. If I want tube sound, I buy tube amps. Why buy a pretender? Buy the real thing.

For me the tubes works way better... i own two mesa rectifiers heads, great stuff, still goes.
I always tend to "catalog" things if you will, for example, i prefer tubes for soloing & riffs, solid state for my chords & power rhythms, but not a definitive thing anyway.
as Richey Boyd stated, modelers have come a long way but still not there, but that's our opinion. go to a music store with a couple of friends and crank everything there as you figure it out for yourself. I'm telling you this 'cause i happen to have a modeler floor unit that isn't quite a solid state nor a tube amp but i like it and, still a choice, an this is what's all about.

My amp is solid state. Because that's how they make 15W amps...
My main unit is an emulator. Simply because my amp doesn't have no magic whatsoever and because the "real thing" is overkill for my needs.

The best kind of amp is the one that spells heaven for you.

I shall do that also... all i have is a modeler amp...
don't know the difference between those solid or tubes anyway :(

In my opinion tubes are the way to go. Modelers come close on heavy distortion but are far away medium distortion and clean sound.

Its just like the other day when I went to a music store and the guy tried to sell me a wah pedal and said it was just as good as a cry baby.

Why buy the imitation when you can buy the real thing?

The only way to get true tube sound is to get a tube amp

I agree with duane and Richey , to me tubes have a warmer rounded tone that I like, however tone is subjective and based on the tone you are trying to achieve solid state or a modeling amp may be better. The Roland JC120 is a solid state amp that many guys used for a long time because it was able to deliver the tone they were looking for or the tone that fit the style of music they were playing at the time. You can not expect the Marshall plexi to be able to get the same tone as a Roland JC120 or vice versa. Modeling amps have made great strides in trying to nail tube tone, they still are not there yet, but they are a great alternative if you like what they do because they usually will not only give you many different amp sounds but will also throw in some effects for free. This can help if the tone your looking for requires a Bradshaw rig and roadie to operate it and all you can afford is a nice combo amp. For my personal use I have five amps and an emulator. You may ask why. Like I said, tone is subjective and they do have different tone. Think of tone as colors and being able to have different ones makes for a more colorful picture. In a large club when playing classic rock I will normally play my Marshall Bluesbreaker or my Mesa boogie Mark III. When I play a country gig I will play My Princeton Reverb. On gigs like private corporate functions I will take my Line 6 Ax2 for the many different tones needed for the many styles of songs and when at home to record in the studio I play my Fender Champion 600, a five watt low priced tube amp for those of you who don't think there is such a thing, or a Behringer V Amp Pro amp emulator . I have even played some gigs that I used no amp and went from my Boss GT6 into a tube compressor straight to the monitor mixer back to my in ears. The point to all of this is there is no " better or worse " but what you like, what you can afford ,what gets the job done and what makes good music.

Here's my thoughts:

Tube - The best all-around choice. Tube circuits have fantastic, natural cleans, screaming overdrive, and a spongy, organic feel that nothing else can reproduce. Crank the gain and drop an overdrive in front, and you're in metal heaven. Keep the overdrive but switch to the clean channel, and classic rock / blues is easy to get.

Solid State - Cleans can be AWESOME on some of these (roland JC-120, anyone?). Distortion can be a little fizzy and harsh sounding, but for a hard-hitting industrial-type sound, it would be the way I would go...were I to do such a tune.

Emulators - Like the old adage: Good at everything, master of nothing. These are great if you're on a budget and need a million sounds at your disposal. Most non-guitar players would never know the difference anyway.

Personally, I'm a hardcore tube guy. I love my marshall and I would never consider getting a solid state (except in the instance above) or a digital emulator. The recorded sound of a tube amp is huge and full of rich harmonics. You just can't beat it.