I have the Beta of DCS, v1.5. It's REALLY nice when it runs. However, it's buggy as hell. I managed to have the SU25T training lessons run reliably. The "create fast mission" does not run at all for me. You must have the 0700 runtimes. I'm sure it will be really excellent when they get it working well. The flying in the SU25T is smoooooth and most lifelike.
ETA: I just did another run and the sense of speed is AMAZING in DCS. FSX can't come close in that department.
I have the Virtavia F86 for FSX. It's pretty good. Bear Studios makes a Mig15 and Mig17. I've not tried them, however. The Mig15 v F86 is the classic dogfighting match.