PS3 is the most viable option. Lets face it XBOX 360 has meager hardware and dismal performance. Current multi-platform games might not be able to produce a discerning difference between the 2 but look at the exclusive and upcoming titles like Gran Turismo 5. It clearly shows the fragment of PS3's power.
Moreover it is being speculated that Microsoft will have to eventually shift to Blu-Ray and at that time XBOX 360 is going to dwindle down under the processing needs as its hardware isn't cut out for such heavy tasks. Also with the limitless customisability and expandability of PS3 its the safest bet. It may not be 'Sasta' but its definitely 'Sunder' and 'Tikaoo' unlike XBOX 360 (read RROD's)