Padraigr - Both Canon and Nikon make excellent cameras, particularly in the DSLR mid-range and higher end, which have features the advanced and professional photographers either want, or actually need for specific purposes, such as full-frame images and other functions.
I'm going for my first DSLR quite soon, and was attracted to the Pentax K-X, now the new K-R. One reason is that all Pentax DSLRs have the stabilising / shake-reduction in the camera body (as do, indeed, Sony DSLRS.)
That means that with Pentax, you don't have to decide, with every new or used lens, whether to get the "standard" model, or the more expensive model, with shake-reduction made-into the lens, as with Canons and Nikons, which don't have shake-reduction in the camera body.
Of course, the more advanced hobbyist Canon / Nikon users know how to shoot with fast shutter-speeds, etc - and can use the un-stabilised lenses very well, or they buy lenses with stabilising built-in. The professionals buy the very best - and quite expensive - lenses, such as Canon's superb "L" range, which "have everything".
However, if you're new to DSLRs, or like me, have a limited income, knowing that every lens you buy, new or second-hand, will be stabilised by the camera itself, is quite an advantage.
That of course does apply to Sony as well as Pentax DSLRS - but Pentax also has another advantage, having been in the Film-SLR and DSLR business for many decades. Every K-mount Film-SLR lens ever made, directly fits onto, and works on, all modern-era Pentax DSLRs - some being semi-manual, others being full-manual - and - they, too, are stabilised by the camera.
There are also the pre K-mount Film-era M42 screw-mount lenses, which fit any Pentax DSLR via an adaptor. There are a lot of Takumar (Asahi-Pentax) M42 lenses still around, at very modest prices, as well as some other brands, such as Tamron. There are also CZ (Carl-Zeiss), and Russian lenses as K-mount and M42.
Some of those are "optically very good glass", at quite low prices. Example - 1972 Takumar Model 2, full SMC, 135mm f/2.5, for just above/below $100.00, depending on condition. That's Asahi-Pentax glass, and all-metal build. Sure, it's a manual lens.... The professional level folk these days wouldn't bother with it - but for hobbyists it's a pretty good option. And $100.00 would hardly buy you a set of lens-caps for a modern-era f/2.5 135mm prime lens. (135mm works as 202.5mm equivalent on a Pentax crop-body.)
Or perhaps an SMC Takumar f/4 300mm prime (450mm equivalent on crop-body) - Asahi optics - for $180.00-$250.00 or so? Yes, manual... But have you priced a "modern-era" f/4 300mm prime, lately?
Obviously, one doesn't "have to" use K-mount or M42 lenses with a Pentax DSLR - there's a good range of modern "auto-everything" lenses from Pentax, Sigma and Tamron, etc, available.
But the options are there, and for we hobbyists and keen amateurs, particularly those with tight family budgets or modest incomes - but also want "good glass" affordably - do present a lot of opportunities.