The most effective 'dilators' that we use are the Champlette and the Champ (no longer available) from Tantus. They are medical grade silicone and tapered to increase your stretch as they go deeper. The Champ goes to about 2+" - so once she's used that puppy on me I'm ready for all the dildos we have (for pegging).
Since she's usually taking me anally - a simple 1.5" butt plug is enough to get her warmed up. Once it goes in and out without much resistance - she's ready for my average sized penis.
BTW - we never use any desensitizing lubes. We always use coconut oil (for both of us). It's body safe, anti-bacterial and lasts a long time. It's also a great moisturizer!