You should price-check meds multiple places -- and factor in shipping costs. Also, Vet-VIPPS membership is something to look for (it's a pharmacy accreditation program guaranteeing legitimate goods are being shipped, so you won't get expired, counterfeit, or gray-market medicine--relatively few online pet pharmacies have earned it). KV has it. I think Valley Vet does too.
KV has free shipping on most items (over $50)--be sure to factor in shipping costs with your price comparison, as they can be high some places. KV has also got very good customer service, any time I've called them. I generally get RX meds from them within a week, as they ship very quickly. The only downside is their website sucks and is very buggy -- I sometimes have to call in the order because the website freezes.
I love when KV offers $10 or $20 KV Bucks on orders over $100 or $150--it makes for great deals on annual meds (like HW prevention). They only do it a few times a year.