In reply to mike.gore:
As a rule of thumb the thicker the rope the more robust the sheath, A 9.8mm rope is a fairly standard diameter for all around climbing. I guess you need to think about the percentage of indoor wall climbing to outdoor you are likely to be doing. If mostly wall then a 10mm to 10.5mm would be harder wearing. Most climbing wall top ropes would easily be thicker and and more furry than this, so I think the belay plate use shouldn't really be a consideration.
As with all things everything is a compromise, but often "performance" often gets the bias over practically. Heavy robust fat ropes aren't sexy, but are pretty much what you need as a first/only rope.
For what it's worth I have a dedicated "fat" 10.5mm wall rope @ 30m for my local wall, and a 9.8mm 60m for not particularly hard outdoor sport climbing.
If I had to have just one rope then a 10mm, rope with a high sheath percentage would be my choice, though I might consider a "Protect" type sheath only treatment and pay a touch more for that.
If you are thinking of redpointing longer hard sports routes then a skinny single is the norm, but will more likely be a "Sunday Best" rope which comes out when needed. For one rope fits all go robust.
Wayne
PS, don't get too hung up on 9.X in reality its hard to see a difference between 9.8 - 10.5, as this diameter is an under tension measurement. In the hand some 9.8mm ropes may feel thicker than a 10mm. Look for a high number of falls, a high sheath percentage, and as impotant one that feels nice!
PPS, might be worth going for dark colour, as light coloured ropes more quickly look grubby/tired with lots of wall use.
PPPS, for the most part trad climbing on a single rope is folly, if moving to outdoor trad getting half ropes early on is a worthy consideration, but I guess that's a whole different topic.
Post edited at 07:45
