Atahualpa to Montezuma, or to ThemeFrame?

Hi all, after being very happy with Atahualpa in flexible width mode, I now want to move on to a theme which displays well on as many devices as possible. I think the jargon is 'responsive'?
I can move to Montezuma and accept a steep learning curve, or I would prefer to move to ThemeFrame and generate my own themes. Which product results in themes that display well on the wider range of devices - ThemeFrame or Montezuma? Thanks for your help with this decision.....

do you want to just use an existing theme, learn how to use it's features (Montezuma) or do the theme development (ThemeFrame)

Thanks for the response, Juggledad - I am wanting to produce four or five web sites for my own business and a friend. Atahualpa has been doing the job just fine, but I want to be sure that mobile devices have a good experience as well. That is my only current motivation for re-working current sites and stepping away from Atahualpa for the new ones - unless it does as well as Montezuma and Themeframe sites with it's range of devices catered for, which I don't think is the case. ThemeFrame is attractive, because I believe, apart from setting up a local server, I can be productive much more quickly - I am happy to learn css and some PHP, but I would rather do that in slow time than against a deadline if I can produce the same result in ThemeFrame. The only 'extras' I would need to install are a polling/survey widget now and a shopping cart/payment system in the future. So, which of the three options - Atahualpa, Montezuma or ThemeFrame gives a good experience over the widest range of devices?

Prepare for a MUCH steeper learning curve with Themeframe, but it will be worth it if you persevere.

Ouch, Jam - thanks for the response - I thought ThemeFrame did not require any coding, or working directly with CSS, let alone PHP - where is the learning curve please? I must have misunderstood the videos.....

Like a lot of things, it's easy once you know how. Themeframe is much the same, but many people have installation/teething problems and need to take time to get familiar with how it works. If users persevere the rewards are great, but new users should accept that they may need to invest several hours to get their head around all it.
You can pop out beautiful themes without CSS coding or any php knowledge with Themeframe. But a better understanding of either will help if you want to develop themes to a higher or more customised level.

Thanks Jam, very helpful. I am expecting to devote quite a few hours to either option! Probably two or three solid days would be optimum, from what you say, by which time I should be productive. So, the original question remains - which serves the widest range of devices? Which has the better responsive web design characteristics please, anyone?