I’ve tried and used a few services and here’s what I’ve found:

1. I’m using my Palm Centro as a modem in order to get onto the internet at all.  Fortunately I’m back on EV-DEVO here – as I think that’s because Alltel merged with Verizon and I’m roaming from Sprint onto their network.
2. I tried GoToMyPC and it worked OK – but I think my Internet connection was slow so that may have been the problem.  My main concern is that it’s at least $10 a month for 1 PC – which is more than I’m willing to pay.
3. I tried LiveMesh – a free service from Microsoft.  This is mainly a file synchronization tool between the “cloud” and multiple PCs. It also has a rudimentary Remote Desktop tool – unfortunately it’s pretty slow.
4. I’m using LogMeIn.com now – and it’s working pretty good.  The basic version (which works for pretty much what I want to do) is free – the pro version (which provides file transfer, remote printing, etc.) is $5 a month for 1 PC.  So right now this is my favorite.
5. For my day job I use the basic Remote Desktop from Microsoft over a VPN – and this works well but requires a Pro windows version and an infrastructure to support it.

The biggest factor will be your internet connection-  as a slow one can make a remote connection very painful….

I’m actually on Sprint – maybe because I live in their home area – but mainly because it’s affordable.  I’ve got my trusty Palm Centro that I only pay between $15-40 a month ($40 is if I’m tethering).  They’re costs are pretty reasonable overall – Verizon or AT&T would cost me more.  I think even if I upgraded my handset it would cost me more.  Ironically I think when I travel I may roam onto Verizon’s network anyway….