Personally i don't see it fair to compare the two as they're totally different beasts.... both of which sound stellar. The Axe as your preamp is more for people who need a lot of very different tones. The Axe is an amazing modeller but with that it can also be very tweak intensive with the bright side of once you have your tone there are no outside influences to change that (bad tubes, weather, bad cables) and its by far way more versitile than any amp i can think of. Now the Roadster to me would be for more a meat and potatoes type player who needs just a couple sounds to do what they need to do. I don't think either wins in terms of tone because both sound stellar.
At the end of the day this is how i think of amps in general... if a amp/modeller has great sound quality and you can conjure the tones you need out of it and it fits into your life financially then it doesnt matter the brand or if it has valves. Also consider the $$$ involved... the Axe Standard is $1500 new, add a good SS power amp or active speaker and your looking at about $2000-2200. I left cab out because both setups would have one. The Roadster is $2000 so off the bat its a little cheaper but now consider the amount and caliber of the fx in the Axe and you'd need to spend at least another $500 if not over $1k. Now to match the Axe's flexibility you'd need to invest in a midi switcher which could run you anywhere from $200-600 for a modest-good unit. Do the math and as you can see if you need everything the axe offers, then financially its the better fit. If your like me you buy the Roadster, the switcher and the Axe and you have it all :twisted: