hosting recommendations

Hi,
As much as I try to minimize plugins and photo sizes, I just can't get past the slowness of our site. Someone recently reported something about "Latency" being really high.

We currently host with psek and I feel like I really need to try a different host.

We do "dynamic subdomain assignment" or something like that - which I know some hosts don't permit. In otherwords, so that we can create newblog.mydomain.tld on the fly.

Please let me know any experience you have with different hosts in terms of performance/speed. The majority of our visitors are in the US but rapidly growing elsewhere.

Thanks in advance